input Null datetime field

Question

I'm using vb.net 2005.  On the iwndow form I have multiple fields that were binded at run time to the SQL server table fields.  Users can add and update the date fine but when then date was changed from a date to a null value the pointer was stuck there.  How can I set those fields to nullable property.

Thanks.
Thuy Tran
202 245-6976