I have approx 6000 pictures in my catalog and I'm slowly working my way through updating keywords and locations. Some have needed to have their metadata updated. I have updated about 2/3rds of them. I now find that, after updating approx 160, the auto-sync just hangs on 162 and I can no longer update any metadata. Updating additional files achieves nothing but increase the no of files needed updating. I get a message that 1 or more files appear to be offline but I have no idea what this file may be. No files have been deleted.