I screwed up last week when I updated how the list that backs the thumbnail grid works. I messed up an optimisation in how it removed certain items, and it caused people popup errors when deleting/removing files. The good news is these errors were just harmless UI side stuff, fixed by re-sorting the page or restarting the client, but I am sorry for the trouble--it is now fixed, and I have some unit tests to make sure it does not happen again.