Web Forms :: What Is The Correct Format For A DateTime String

In a simple ASPX page, I have an SqlDataSource and a DataList control bound to it.It shows 3 columns; UserName, DateTimeStamp, and Comment.The database table has these defined as nvarchar(24), datetime, and nvarchar(80).The UserName and DateTimeStamp are shown in the ItemTemplate as Labels, while the Comment is a multiline TextBox.I have an event handler for the OnTextChanged for the Comment so that I can update the table as soon as the user tabs off the TextBox.I use the UserName and DateTimeStamp as the Primary Key, and pass all 3 to a stored procedure, where the parameters are declared the same types as the table.What I'm getting though is an "Input string was not in the correct format", which can only be the DateTime that I am passing.

I've tried different date/time formats, but so far come up empty as to the one that will actually work from the C# code.All the different formats I've tried work fine if I pass them to the SP directly via Management Studio, but all throw an error when I use

SqlDataSource.UpdateParameters.Add("DateTimeStamp", System.Data.DbType.DateTime, lblDateTimeStamp.Text);