I have a Numbers document that I update monthly. I updated it, but when I went to save it, a notice says "xxxxx.numbers could not be saved". I tried a Save As xxxxx2.numbers, but it would not allow that either. I went to Get Info, and it says I have custom access, and Read and Write Privilege. I went to other recent numbers documents and they save fine. Seems to be only this document. What gives? Mac OS 10.11.6