I was using AutoCAD 2017 then it started bring ing this "Fatal Error" message after starting it and working on it for a few minutes. I upgraded to AutoCAD 2021 but am still experiencing the same problem. Someone please advice, it is really frustrating me. 🙁
You should check the status of your drawing file. I experienced the same issue with AutoCAD '15. Try using the Audit command, then purge all. It should work.