by Emma Richardson.
Can you show us your settings page? I had this happen once and was shocked to discover that I did not get an error message and Moodle just randomly decided to save them somewhere else (however, that also saved my butt when I needed to restore a course!) . In my situation, I was using a folder that was on another server mounted to my moodle server - the mount had disconnected. Moodle could still see the folder where I mount the remote folder and thought it was good but could not write to it because the remote server was disconnected.