Hi, I'm running a Lightroom 5.7 on a Mac (OS,X,10.7.5) and have a problem with a catalog. The catalog opens and I can see all of my images with all adjustments but when I try to do any work on them (i.e. spot removal) I get a message saying "Lightroom encountered an error when reading a catalog file and needs to quit. Lightroom will attempt to diagnose the problem the next time it launches." I then get a message saying "Lightroom encountered an error when reading a catalog file and needs to quit." and the whole problem begins again. I don't have access to previous recent backup and I've tried backing up the catalog to a different folder and drive...is there anything I can do? PS I'm not good with computers/software so if anyone can help please keep it as simple as possible and not too technical.