InvalidCastException: Unable to cast object of type 'System.String' to type 'System.Int32'

I am trying to display the result from the database to the user on the front end but I keep getting the following exception:

InvalidCastException: Unable to cast object of type 'System.String' to type 'System.Int32'

and

System.InvalidOperationException: 'An exception occurred while reading a database value for property 'CList.CourseCategory'. The expected type was 'LearnAngebot.Models.Courscategory' but the actual value was of type 'System.String'.'

I am lost as to what has gone wrong.

I have a similar code to display the courses and it seems to be working fine. I used the same format for this but keep getting this error.

The C# code:

public class IndexModel : PageModel
{
    public CUser User { get; set; }
    public bool empty { get; set; }

    public readonly IHostingEnvironment _env;
    private readonly CDataContext _context;
    private readonly IUserService _UserService;

    public IndexModel(CFE_CrazyLabContext context, IUserService UserService, IHostingEnvironment hostingEnvironment)
    {
        _env = hostingEnvironment;
        _context = context;
        _UserService = UserService;
        User = UserService.GetUser();
    }

    public IList<CList> ResultList { get; set; }
    public CUser StudentUser { get; set; }
    public CStudent Student { get; set; }

    public void LoadList(CList list)
    {
        StudentUser = _UserService.GetUser(list.StudentUser);
    }
    public void OnGet()
    {
        ResultList = _context.Result.Where(o => EF.Functions.Like(o.StudentUser, User.UserName)).ToList();

    }
}

HTML code:

@if(Model.ResultList.Count == 0)
{
<div>
    <h2> No Result yet </h2>
</div>
}

@if(Model.ResultList.Count > 0)
{
    <div class="Custom-Table Custom-Table-Big">
    <table>
        <tbody>
            <tr id="head">
                <th><a href="index.pgp?">Student UserName</a></th>

                <th><a href="index.php?">Course Name</a></th>

                <th><a href="index.pgp?">Category</a></th>

                <th><a href="index.pgp?">Date</a></th>
            </tr>

            @foreach(var item in Model.ResultList)
            {
                Model.LoadList(item);
                <tr>
                    <td>
                        @item.StudentUser
                    </td>

                    <td>
                        @item.CourseName
                    </td>

                    <td>
                        @item.CourseCategory
                    </td>

                    <td>
                        @item.Date
                    </td>
                </tr>
            }
        </tbody>
    </table>
</div>
}

Why exactly am i getting this exception and how do I resolve it? Thanks in advance.