HELP - Form will not allow me to Add or Delete or Rename fields - ???

HELP - Form will not allow me to Add or Delete or Rename fields - ???

I have a large app that I've been creating. I made good progress until now when I've encountered several serious bugs. I really need your help. I've got tons of hours invested and I can't go further. 1 - One of my forms will not allow me to add any more fields, and it wont' let me delete certain fields either. Each time I try to do a delete, it complains. If I try to rename, and/or hide the field, it says ok, but those changes do not stick. Help!