just a wild one
someone has the table you are trying to base the form design on open.
Either you've got it open with the table designer, a query using that table is open
OR someone else has got the table open or a query using the table open.
close down all table & query designers, all forms not being used right now, then try again
its a good reason to develop on a totally separate db form a production db, and ideally only one person be devloping in any one area (you can have multiple people developing access forms & reports but it needs good itner team discipline on booking work in and out.
there is a possibility that your copy of Access may have got corrupted
I'd rather be riding on the Tiger 800 or the Norton