Thank you for the response. I'm on Windows 10 pro, version 20H2, Intel(R) Core(TM) i9-9900K CPU @ 3.60GHz 3.60 GHz, 128GIG RAM. This is MSI GT70 Titan DT95G machine.
I was working on my file with no issues. Then tried to export an STL file but it failed. Tried many times but all failed. So I decided to close the program. After that the file won't open. I can open other files but not this one. After it fails to open I also see a message that says "reference is missing".
There are 72 versions of the file and I found out I can open up to version 59. Anything above that won't open. I remember that at version 60 I inserted another file into the project (insert into project). Maybe this is the cause? But that file is still around and hasn't been erased. So I don't know what the problem is.
