Bill,

I cam across the same error.

I don't know that this is the case for you (or even a valid issue), but I was getting the error on any form that had the mmDropDownList (or alike). I had not, in previous versions, set the BindingValueSource or BindingValueSourceMember properties. So, in the end, after iisreset, rebooting, manually deleting the "Temporary ASP.NET Files" contents, and setting 6 Binding properties, my troubles went away.

(hope this isn't worthless info)

Mike