Exception:Failed To Convert Parameter Value From A Guid To A String?

I have a problem while creating a web application using LinqTemplate here is the explanation step wise....
1.I have created a database with a table name UserTest with one column name UserId with uniqidentifier datatype2. I have created a classLiberary Project where i have used LinqTemplate of subsonic for code Generation of DAL and created a partial class for UserTest

public partial class TestUser:Classes
{
public int Insert(TestUser user)

[code]...

Now when I Build the project it build successfully and when i run the project it shows
the UserTest.aspx page with a button but when i click on button it must insert the new guid value into the table butit throws an exception

[InvalidCastException: Object must implement IConvertible.]
System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider) +2560525
System.Data.SqlClient.SqlParameter.CoerceValue(Object value, MetaType destinationType) +414
[InvalidCastException: Failed to convert parameter value from a Guid to a String.]
TestPages.UserEdit.btnCreateNewAccount_Click(Object sender, EventArgs e) in D:TestPagesUserEdit.aspx.cs:61
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +105