Yes, I should have been more specific. I removed .vpj, .vpw, .vpwhist, and .vtg.
If I remote login from another machine and use the 16.0.3 installation I have on this machine to create the project in the same folder, it works. So it's probably some file in the My SlickEdit Config folder that is corrupt. I'm just not familiar enough with the function of each file to know which one. I tried deleting vslick.sta, but that didn't help.