Hi Shelley,
It's a little hard to know what the issue is here based off the error you are receiving. If you have reverted back to the stock screen and are still having this issue, there could be more to it. My first suggestion would be to first try regenerating the table you have set for the screen causing the issues. Go to Customize->Tables/Fields, click "Edit Fields..." on the table, then once you get the pop-up screen, simply click "Finished Editing Fields", this action will regenerate that specific table.
If the suggestion above doesn't help resolve your issue, I would suggest you send me a private email either here in the forums, or at b.citren@method.me so that I can double check your stock screen and see what is going on here. In your email, please include your Contact Details, CompanyAccount name, and the screens you are having the issue with. You will also need to turn on MethodSupport, this can be done by going to Customize->Users, look for the MethodSupport user in the 2nd section of the screen and make sure there is a checkmark in the "Active" column.
-Ben