I've been renaming my files as .accdr for years now without a problem. I have been working in A2010 even though my users all have A2013. Last week, I got "upgraded" to O2013 and now I can't rename my databases as .accdr!!!!!!!!!!!!!!!!!! Has anyone seen this? I have tried all their suggestions including the /runtime command switch to no avail. Once I rename a database, I can no longer open it. That includes ALL .accdr's, not just the one I created this week. My second computer, which has been A2013 all along still works fine. However, some of the users are now getting the error so I'm afraid it was caused by a patch since the impact is spotty. But I can't identify any patches that were applied this week. We all have the same version info and are all using Win 7.