Why does this sql function not work with REPLACE?

I am having a problem with my sql function. The following function operates as expect but when I substitute, it only returns one row:

CAST(t.ColumnName as nvarchar(100)) 

for:

REPLACE(CAST(t.ColumnName as nvarchar(100)), 'ID', 'Id')

What is wrong? Here is my calling code:

PRINT dbo.CreatePocoFromTable('dbo.OnePoundFish')

Here is the function itself:

CREATE FUNCTION [dbo].[CreatePocoFromTable]
    (@SchemaAndName nvarchar(200))
RETURNS Nvarchar(MAX) AS
BEGIN
/* Example call:

PRINT dbo.CreatePocoFromTable('dbo.OnePoundFish')

*/

DECLARE @TableName NVARCHAR(100) = SUBSTRING(@SchemaAndName , CHARINDEX('.', @SchemaAndName ) + 1, LEN(@SchemaAndName ))   
DECLARE @TableSchema NVARCHAR(100) = SUBSTRING(@SchemaAndName , 1, CHARINDEX('.', @SchemaAndName ) - 1)  
DECLARE @result Nvarchar(max) = ''

SET @result = @result + 'using System;' + CHAR(13) + CHAR(13) 

IF (@TableSchema IS NOT NULL) 
BEGIN
    SET @result = @result + 'namespace ' + @TableSchema  + CHAR(13) + '{' + CHAR(13) 
END

SET @result = @result + 'public class ' + @TableName + CHAR(13) + '{' + CHAR(13) 

SET @result = @result + '#region Instance Properties' + CHAR(13)  

SELECT @result = @result + CHAR(13) 
    -- BL/DAL/DataRepository Entity attributes
    + '[DataField("' + t.ColumnName + '")]' + CHAR(13)
    + ' public ' + t.ColumnType + ' ' + CAST(t.ColumnName as nvarchar(100)) + ' { get; set; } ' + CHAR(13) 

FROM
(
    SELECT  
        c.COLUMN_NAME   AS ColumnName 
        , CASE c.DATA_TYPE   
            WHEN 'bigint' THEN
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'Int64?' ELSE 'Int64' END
            WHEN 'binary' THEN 'Byte[]'
            WHEN 'bit' THEN 
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'Boolean?' ELSE 'Boolean' END            
            WHEN 'char' THEN 'String'
            WHEN 'date' THEN
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'DateTime?' ELSE 'DateTime' END                        
            WHEN 'datetime' THEN
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'DateTime?' ELSE 'DateTime' END                        
            WHEN 'datetime2' THEN  
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'DateTime?' ELSE 'DateTime' END                        
            WHEN 'datetimeoffset' THEN 
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'DateTimeOffset?' ELSE 'DateTimeOffset' END                                    
            WHEN 'decimal' THEN  
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'Decimal?' ELSE 'Decimal' END                                    
            WHEN 'float' THEN 
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'Single?' ELSE 'Single' END                                    
            WHEN 'image' THEN 'Byte[]'
            WHEN 'int' THEN  
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'Int32?' ELSE 'Int32' END
            WHEN 'money' THEN
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'Decimal?' ELSE 'Decimal' END                                                
            WHEN 'nchar' THEN 'String'
            WHEN 'ntext' THEN 'String'
            WHEN 'numeric' THEN
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'Decimal?' ELSE 'Decimal' END                                                            
            WHEN 'nvarchar' THEN 'String'
            WHEN 'real' THEN 
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'Double?' ELSE 'Double' END                                                                        
            WHEN 'smalldatetime' THEN 
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'DateTime?' ELSE 'DateTime' END                                    
            WHEN 'smallint' THEN 
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'Int16?' ELSE 'Int16'END            
            WHEN 'smallmoney' THEN  
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'Decimal?' ELSE 'Decimal' END                                                                        
            WHEN 'text' THEN 'String'
            WHEN 'time' THEN 
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'TimeSpan?' ELSE 'TimeSpan' END                                                                   

            WHEN 'timestamp' THEN 
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'DateTime?' ELSE 'DateTime' END                                    
            WHEN 'tinyint' THEN 
                CASE C.IS_NULLABLE
                    WHEN 'YES' THEN 'Byte?' ELSE 'Byte' END                                                
            WHEN 'uniqueidentifier' THEN 'Guid'
            WHEN 'varbinary' THEN 'Byte[]'
            WHEN 'varchar' THEN 'String'
            ELSE 'Object'
        END AS ColumnType
        , c.ORDINAL_POSITION 
FROM    INFORMATION_SCHEMA.COLUMNS c
WHERE   c.TABLE_NAME = @TableName and ISNULL(@TableSchema, c.TABLE_SCHEMA) = c.TABLE_SCHEMA  
) t
ORDER BY t.ORDINAL_POSITION

SET @result = @result + CHAR(13) + '#endregion Instance Properties' + CHAR(13)  

SET @result = @result  + '}' + CHAR(13)

IF (@TableSchema IS NOT NULL) 
BEGIN
    SET @result = @result + CHAR(13) + '}' 
END

  RETURN @Result
END

Thanks :)