Give the info below a try just in case cache files are in conflict with your project.
A repair I do if any issue crops up, is to shut down the project, then in Windows Explorer, go into the project folder, open the cache folder, and blow away all files in that cache folder, they will be rebuilt on the next start up.
The next thing I do is go to the projects Tag folder, and look for one file with "the project name".cac
I THEN BLOW THAT ONE ONLY AWAY, leaving all the other files in that folder, this .cac file also will be rebuilt on project start up.
Then shut down computer and reboot and run your project.
I cant promise this will fix your problem, but it wont harm it either.
The Harmony files for RSLinx they are also cache files that get rebuilt on start up.
If you havebeen doing alterations
Its also possible that the you have a corrupted tag data base and will need to export the tag data base and re import them but in my case that was at software version change many years ago