Saving new doc in pages

I have an iMac, 2.5 GHz Intel Core i5. Tonight, when I tried to save a new Pages document I got a message that said, "An error occurred while reading: Operation not permitted." I am using Pages 5.5.3. I use it every day, and have had no trouble in the past with saving documents. I tried different document names (including "Untitled"), and different locations (including Desktop). The document will not save. I am not having this problem with other applications.