update method not working with date/time fields in access database

[pardede]

This may be a long shot. Try to put some checking before the real update method, that converts the empty string to a null, like:

If txtDateComplete.Text = "" Then
   Data1.Recordset!date_complete = Null
End If

Once again it's a shot (also i might have some syntax error in code above), but the general idea is to avoid sending nullstring to the database.

Maybe you could also check the 'required' and 'allowzerolength' property of the field in the .mdb