Excel Memory Issue

Hello. As soon as I enter data into an Excel sheet, or when I try to save one, I receive the message "Microsoft Excel cannot open or save any more documents because there is not enough memory or available disk space". However, there is plenty of both. I suspect it is an iOS issue rather than an Excel issue because it only happens on one user account? I have updated office and repaired disk permissions but it is still occuring. Any guidance gratefully received!

Thanks...