from XML to structure using XML serialzation C#

Your initial problem is as follows:

1. Your List<Project> LProject; needs to be public, and to be marked with [XmlElement] to indicate it should be serialized without an outer container element:

   // Fixed - made public and marked with [XmlElement]
   [XmlElement("Project")]
   public List<Project> LProject;
   

   XmlSerializer only serializes public properties and fields, even if marked with an XML serialization attribute.

However, after I had fixed this and attempted to deserialize the sample XML, I found many more problems:

2. There were several duplicate copies of the type NameElement throughout your class hierarchy. This causes XmlSerializer to throw the following exception:

   // InnerException: System.InvalidOperationException
   // Message="Types 'Question42409171.XMLStructure.Project.Package.NameElement' and 'Question42409171.XMLStructure.Project.NameElement' both use the XML type name, 'NameElement', from namespace ''. Use XML attributes to specify a unique XML name and/or namespace for the type."
   

   The solution is to eliminate the duplicates and retain one single definition:

   // Fixed - removed duplicates.
   // InnerException: System.InvalidOperationException
   // Message="Types 'Question42409171.XMLStructure.Project.Package.NameElement' and 'Question42409171.XMLStructure.Project.NameElement' both use the XML type name, 'NameElement', from namespace ''. Use XML attributes to specify a unique XML name and/or namespace for the type."
   public class NameElement 
   {
       // Fixed
       // This was marked as an element but should be an attribute
       [XmlAttribute("name")]
       public string name;
   
       public NameElement()
       {
           name = "";
       }
   }
   

3. In NameElement, name should be marked with [XmlAttribute] not [XmlElement], as shown above.

4. Several properties are missing from Project:

       // Fixed missing property
       [XmlElement("Defines")]
       public NameElement Defines;
   
       // Fixed missing property
       [XmlElement("Make")]
       public NameElement Make;
   
       // Fixed missing property
       [XmlElement("Include")]
       public NameElement Include;
   

5. In Package several complex properties are marked with [XmlAttribute]. Only simple properties (those that can be converted to strings) can be so marked. These properties need to be marked with [XmlElement]:

           // InnerException: System.InvalidOperationException
           // Message="Cannot serialize member 'Release_path' of type Question42409171.XMLStructure.Project.Package.NameElement. XmlAttribute/XmlText cannot be used to encode complex types."
           [XmlElement("Release_path")]
           public NameElement Release_path;
   
           // Fixed
           // InnerException: System.InvalidOperationException
           // Message="Cannot serialize member 'Rsu_path' of type Question42409171.XMLStructure.NameElement. XmlAttribute/XmlText cannot be used to encode complex types."
           [XmlElement("Rsu_path")] // Fixed 
           public NameElement Rsu_path;
   

6. In MigrationAndDevicesBin the property _Device needs to be marked with [XmlElement] not [XmlArray]:

       public class MigrationAndDevicesBin
       {
           [XmlAttribute("name")]
           public string name;
   
           [XmlAttribute("exec")]
           public string exec;
   
           // Fixed - should be [XmlElement]
           [XmlElement("Device")]
           public List<Device> _Device;
   

7. In SerialFlashHexImage the nested type File was never even used. A property public List<File> Files { get; set; } is required:

       public class SerialFlashHexImage
       {
           [XmlAttribute("name")]
           public string name;
   
           [XmlAttribute("exec")]
           public string exec;
   
           // Fixed - the type File was not even used!
           [XmlElement("File")]
           public List<File> Files { get; set; }
   
           public SerialFlashHexImage()
           {
               this.Files = new List<File>();
               name = "";
               exec = "";
           }
   

8. In Flasher, properties corresponding to name and exec are missing:

       public class Flasher
       {
           // Fixed - missing attribute
           [XmlAttribute("name")]
           public string name;
   
           // Fixed - missing attribute
           [XmlAttribute("exec")]
           public string exec;
   

9. Also in Flasher, items needs to be a collection, not a singleton:

       public class Flasher
       {
           //Fixed
           //InnerException: System.InvalidOperationException
           //Message="For non-array types, you may use the following attributes: XmlAttribute, XmlText, XmlElement, or XmlAnyElement."
           [XmlElement("Item")]
           public List<Item> items;
   

And that is as far as I got. Sample fiddle. The XML can be loaded successfully and most of the data appears to be present, but I did not debug it completely as doing so is outside the scope of a stackoverflow question.

Quite honestly, that's too many problems. I recommend you abandon this attempt to manually create c# classes to deserialize this XML, and instead create classes using an automated code-generation tool such as https://xmltocsharp.azurewebsites.net/ or Paste XML as Classes.

Here are my final modifications to your types:

[XmlRoot("MotProjects")]
public class XMLStructure
{
    // Fixed - made public and marked with [XmlElement]
    [XmlElement("Project")]
    public List<Project> LProject;

    public XMLStructure()
    {
        LProject = new List<Project>();
    }

    // Fixed - removed duplicates.
    // InnerException: System.InvalidOperationException
    // Message="Types 'Question42409171.XMLStructure.Project.Package.NameElement' and 'Question42409171.XMLStructure.Project.NameElement' both use the XML type name, 'NameElement', from namespace ''. Use XML attributes to specify a unique XML name and/or namespace for the type."
    public class NameElement 
    {
        // Fixed
        // This was marked as an element but should be an attribute
        [XmlAttribute("name")]
        public string name;

        public NameElement()
        {
            name = "";
        }
    }

    public class Project
    {
        [XmlAttribute("name")]
        public string name;

        [XmlAttribute("exec")]
        public string exec;

        // Fixed missing property
        [XmlElement("Defines")]
        public NameElement Defines;

        // Fixed missing property
        [XmlElement("Make")]
        public NameElement Make;

        // Fixed missing property
        [XmlElement("Include")]
        public NameElement Include;

        [XmlElement("Ref_mot")]
        public NameElement Ref_mot;

        [XmlElement("Folder")]
        public NameElement Folder;

        [XmlElement("MotCommand")]
        public NameElement MotCommand;

        [XmlElement("Param4MotCommand")]
        public NameElement Param4MotCommand;

        [XmlElement("ExtraDefine")]
        public NameElement ExtraDefine;

        [XmlElement("Package")]
        public Package MYPackage;

        [XmlElement("MotImage")]
        public MotImage Mot_Image;

        [XmlElement("MigrationAndDevicesBin")]
        public MigrationAndDevicesBin _MigrationAndDevicesBin;

        [XmlElement("SerialFlashHexImage")]
        public SerialFlashHexImage MYSerialFlashHexImage;

        [XmlElement("Flasher")]
        public Flasher MFlasher;

        public Project()
        {
            name = "";
            exec = "";
            Include = new NameElement();
            Ref_mot = new NameElement();
            Folder = new NameElement();
            MotCommand = new NameElement();
            Param4MotCommand = new NameElement();
            ExtraDefine = new NameElement();
            Mot_Image = new MotImage();
            MYPackage = new Package();
            _MigrationAndDevicesBin = new MigrationAndDevicesBin();
            MYSerialFlashHexImage = new SerialFlashHexImage();
            MFlasher = new Flasher();
        }

        public class MotImage
        {
            [XmlAttribute("name")]
            public string name;

            [XmlAttribute("exec")]
            public string exec;

            [XmlElement("Boot_path")]
            public NameElement Boot_path;

            [XmlElement("Rsu_path")]
            public NameElement Rsu_path;

            [XmlElement("Release_path")]
            public NameElement Release_path;

            [XmlElement("Image_path")]
            public NameElement Image_path;

            [XmlElement("Catalog_number")]
            public NameElement Catalog_number;

            [XmlElement("Additional_text")]
            public NameElement Additional_text;

            public MotImage()
            {
                name = "";
                exec = "";
                Boot_path = new NameElement();
                Rsu_path = new NameElement();
                Release_path = new NameElement();
                Image_path = new NameElement();
                Catalog_number = new NameElement();
                Additional_text = new NameElement();
            }
        }

        public class Package
        {
            [XmlAttribute("name")]
            public string name;

            [XmlAttribute("exec")]
            public string exec;

            // Fixed
            // InnerException: System.InvalidOperationException
            // Message="Cannot serialize member 'Release_path' of type Question42409171.XMLStructure.Project.Package.NameElement. XmlAttribute/XmlText cannot be used to encode complex types."
            [XmlElement("Release_path")]
            public NameElement Release_path;

            // Fixed
            // InnerException: System.InvalidOperationException
            // Message="Cannot serialize member 'Rsu_path' of type Question42409171.XMLStructure.NameElement. XmlAttribute/XmlText cannot be used to encode complex types."
            [XmlElement("Rsu_path")] // Fixed 
            public NameElement Rsu_path;

            [XmlElement("Migration_path")]
            public NameElement Migration_path;

            [XmlElement("Default_path")]
            public NameElement Default_path;

            [XmlElement("Old_Release_path")]
            public NameElement Old_Release_path;

            [XmlElement("Old_Default_path")]
            public NameElement Old_Default_path;

            [XmlElement("Package_path")]
            public NameElement Package_path;

            [XmlElement("Additional_text")]
            public NameElement Additional_text;

            [XmlElement("Catalog_number")]
            public NameElement Catalog_number;

            public Package()
            {
                name = "";
                exec = "";
                Release_path = new NameElement();
                Rsu_path = new NameElement();
                Migration_path = new NameElement();
                Default_path = new NameElement();
                Old_Default_path = new NameElement();
                Old_Release_path = new NameElement();
                Rsu_path = new NameElement();
                Release_path = new NameElement();
                Catalog_number = new NameElement();
                Additional_text = new NameElement();
            }
        }

        public class MigrationAndDevicesBin
        {
            [XmlAttribute("name")]
            public string name;

            [XmlAttribute("exec")]
            public string exec;

            // Fixed - should be [XmlElement]
            [XmlElement("Device")]
            public List<Device> _Device;

            [XmlElement("Catalog_number")]
            public NameElement Catalog_number;

            [XmlElement("OutputFile")]
            public OutputFile OutPutFile;

            public MigrationAndDevicesBin()
            {
                name = "";
                exec = "";
                _Device = new List<Device>();
                Catalog_number = new NameElement();
                OutPutFile = new OutputFile();
            }
        }

        public class Device
        {
            [XmlAttribute("id")]
            public string id;

            [XmlAttribute("productType")]
            public string productType;

            [XmlAttribute("swVersion")]
            public string swVersion;

            [XmlAttribute("pathname")]
            public string pathname;


            public Device()
            {
                id = "";
                productType = "";
                swVersion = "";
                pathname = "";
            }
        }

        public class OutputFile
        {
            [XmlElement("pathname")]
            public string pathname;

            public OutputFile()
            {
                pathname = "";
            }
        }

        public class SerialFlashHexImage
        {
            [XmlAttribute("name")]
            public string name;

            [XmlAttribute("exec")]
            public string exec;

            // Fixed - the type File was not even used!
            [XmlElement("File")]
            public List<File> Files { get; set; }

            public SerialFlashHexImage()
            {
                this.Files = new List<File>();
                name = "";
                exec = "";
            }

            public class File
            {
                [XmlAttribute("name")]
                public string name;

                [XmlAttribute("exec")]
                public string exec;

                [XmlAttribute("id")]
                public string id;

                [XmlAttribute("fileType")]
                public string fileType;

                [XmlAttribute("pathname")]
                public string pathname;

                [XmlElement("OutputFile")]
                public OutputFile OutputFile;

                [XmlElement("Catalog_number")]
                public NameElement Catalog_number;

                public File()
                {
                    name = "";
                    exec = "";
                    id = "";
                    fileType = "";
                    pathname = "";
                    OutputFile = new OutputFile();
                    Catalog_number = new NameElement();
                }
            }
        }

        public class Flasher
        {
            // Fixed - missing attribute
            [XmlAttribute("name")]
            public string name;

            // Fixed - missing attribute
            [XmlAttribute("exec")]
            public string exec;

            //Fixed
            //InnerException: System.InvalidOperationException
            //Message="For non-array types, you may use the following attributes: XmlAttribute, XmlText, XmlElement, or XmlAnyElement."
            [XmlElement("Item")]
            public List<Item> items;

            public Flasher()
            {
                items = new List<Item>();
                name = "";
                exec = "";
            }

            public class Item
            {
                [XmlAttribute("name")]
                public string name;

                [XmlAttribute("value")]
                public string value;

                public Item()
                {
                    name = "";
                    value = "";
                }
            }
        }
    }
}