Kevin,

I thought I had it figured out but I'm still getting the same error. I think at least part of the problem was that when I ran the Business Layer Generator, it called the GetNonNullableDbValue function for each of the fields. I changed that to GetNullableDbValue for all the fields that can be blank, including all the date fields. If I leave a date field blank, I still get the MM error message:
"String was not recognized as a valid DateTime."

I also tried unsuccessfully adding the following code to the click method of my save button right before calling the save method:

        if (mmType.IsEmpty(this.txtBirthDate.Text))
            dsPersonnel.Tables[0].Rows[0]["birthdate"]= DBNull.Value;

What next?

Thanks.

Linda