Batch rename not working

Suddenly batch renaming is not working. When I select a group of images in the capture folder browser, then right click to batch rename, I keep getting a dialogue box showing me a list of all the images selected saying "could not rename file".

This is a huge problem because I have to go into Photo Mechanic to rename images then when I come back to C1 all my image settings are wiped out. I've been renaming images in the browser for a very long time and have never had a problem and I'm not doing anything different.