InvalidCastException on LINQ-2-SQL Model When Inserting

I am getting an InvalidCastException when trying to insert an item into a database using LINQ-to-SQL. As far as I can tell, everything is the proper type.

The SQL table is (abridged):

CREATE TABLE [dbo].[Timer](
    [TimerId] [int] IDENTITY(1,1) NOT NULL,
    [UserName] [nvarchar](64) NOT NULL,
    [TimeStamp] [datetime] NOT NULL,
    [SessionId] [uniqueidentifier] NOT NULL,
    [Action] [nvarchar](50) NOT NULL,
    [ActionId] [uniqueidentifier] NOT NULL,
    [Description] [nvarchar](256) NOT NULL,
 CONSTRAINT [PK_T开发者_开发技巧imer] PRIMARY KEY CLUSTERED 
(
    [TimerId] ASC
)

The LINQ model is (abridged):

public partial class Timer
{

    [Column(AutoSync=AutoSync.OnInsert, DbType="Int NOT NULL IDENTITY", IsPrimaryKey=true, IsDbGenerated=true)]
    public int TimerId { get; set; }

    [Column(DbType = "NVarChar(64) NOT NULL", CanBeNull = false)]
    public string UserName { get; set; }

    [Column(DbType = "DateTime NOT NULL")]
    public DateTime TimeStamp { get; set; }

    [Column(DbType = "UniqueIdentifier NOT NULL")]
    public Guid SessionId { get; set; }

    [Column(DbType = "NVarChar(50) NOT NULL", CanBeNull = false)]
    public string Action { get; set; }

    [Column(DbType = "UniqueIdentifier NOT NULL")]
    public Guid ActionId { get; set; }

    [Column(DbType = "NVarChar(256) NOT NULL", CanBeNull = false)]
    public string Description { get; set; }

}

And the offending code is (abridged):

using (var ctx = new MyDataContext())
{
    var timer = new Timer();
    timer.Action = "Start";
    timer.ActionId = Guid.NewGuid();
    timer.Description = "foo";
    timer.SessionId = Guid.NewGuid();
    timer.TimeStamp = DateTime.UtcNow;
    timer.UserName = "foo";

    ctx.Timers.InsertOnSubmit(timer);
    ctx.SubmitChanges();  // exception thrown here
}

The error message says System.InvalidCastException: Specified cast is not valid. but it doesnt mention which property is causing the problem. Can anyone spot which property is causing me problems?

---

You might want to either:

1) Change TimeStamp data type to DateTime2 - SQL Server 2008 only.

or

2) Change timer.TimeStamp = DateTime.UtcNow; to timer.TimeStamp = DateTime.Now.ToUniversalTime();

---

I dropped the table, recreated it, refreshed my model and everything started working without having to change anything else. I dont think anything changed, but clearly .NET likes me again.

---

I solved that problem by setting the Server Data Type property to uniqueidentifier in my DBML.