That's something that happens that is peculiar to PLC 5's. Upload a copy of the program from the controller, save it. Then, wipe the controller by powering it down, pull the battery, and short the battery contacts for a minute. Download a fresh copy of your program, then do your edits again.
By the way... is the controller keyswitch in program mode? Certain things you can't do on PLC 5's in rem/run. Stuff like creating new data table addresses, for one popular example.
One reason not to give DIY advice:
Catch a man a fish and you can sell it to him.
Teach a man to fish and you’ve ruined a good business opportunity.