What that is saying is the program that was last compiled differs from the one in the PLC, so at some point there was a change that is in the PLc or in the original file that has changed and has not been downloaded. revert back to the original file i.e. before the change then do a compare, check differences (it may be only a compile time/date but the logic could be the same. In this case you may need to compile the whole program & download it. This is a lesson for you, firstly if you make on-line changes always save the project, when finished for the day do a compare to check the file & PLC match, always before starting a new session save a backup before doing any mods, ideally keep a few backups so you can go back a few sessions.
I suggest you go back before the latest mods, do a compare it may only complain the compile dates are different, in that case, put the mods in but you will have to do a download not an on-line change, lonly download the program file do not select device memory as any changes in values in these memories will be overwritten, It is a good idea at the end of the day to update the device memory on the file by uploading it from the PLC.
