User was attempting to assign metadata to a group of documents (12) within a folder. Please see the screenshots below for the error message on the fields side as well as the document list. I was able to verify from the management panel that the only user logged into the repository at the time was the user having the issue. It did show one of the documents in this list was locked by that user, but she did not have it open and had not had it open at all that day. Unlocking it from the management panel did not resolve the issue right away - same message on her next attempt. Several minutes later I went to do the exact same thing she was trying to do with the documents and had no problem.  

I used Audit Trail to see if the document showing as locked had been opened previously, thinking maybe someone had opened it and left it open before. Since it came over from a large set of documents that we migrated to the repository at once, it had never been opened.