I was getting this prompt. From a search of the Tek-tips forum, a lot of people get it, in totally different situations, and virtually none of the posts were replied to. It seems to be the Access equivalent of a nervous breakdown or something.
JuanLoco (Visitor) says "I fixed it by making a copy of the offensive form, deleting the original, and then renaming the copy to the original name."
Well, chapter two here. JuanLoco's suggestion helped, but my app went south again after adding one record. Happened repeatedly until I:
made a blank db,
imported all but the offending form and two ODBC links that seemed to be getting trashed as well,
rebuilt the links to the two tables on the back end (don't import and use Linked Table Manager -- delete 'em and make the links again: the problem seemed to be related to Access losing track of the unique fields in the backend tables when the offending form was used.)
and finally went back to the original database, copied the offending form, and pasted it into the new database.
Importing the form directly didn't work, and neither did importing the links and using Linked Table Manager. Very odd. Wierd and scary. But it's working now, and seems stable.