Hi,
I think I used both unity plugin (the project view) and windows explorer to move the files.
Under Resources/, I had 3 folders with sounds. I moved all folders under a single folder. I changed also some other files.
Then the check in gave the error message. When I copied all the sounds folders in their original places, the message disappeared and I was able to commit. Then I was able to delete the copied folders and check in without error messages.
I'll check if I can reproduce it to give you a more step by step approach with screenshots.
Pierre