It worked! I guess I was overcomplicating it, eh? Here's how it reads now, which may well have been the way the builder set it up for me in the first place before I decided to mess it up.

   <mm:mmTextBox ID="mmTextBox1" runat="server" 
        BindingSource="Customer" BindingSourceMember="txtMailAdd1" 
        BindingSourceType="Default"></mm:mmTextBox>

Oh, and about those fieldnames (eg. txtMailAdd1)...isn't that lovely? Those are the fieldnames I inherited with this app. I'm not sure what the original developer was thinking, but it's definitely going to create some confusion for me.

Thanks for your help, Tim.

Eric