If it pops up the next time you run, try deleting your th143.cfg config file. Given what you've said, it's probably the same issue a number of others have, and it's generally solved by:
a) changing the resolution in the config, running, then changing back
b) if not, deleting the thxx.cfg file
Usually "just reinstall" works too but likely because it gives you a new config file. This was also probably the same issue you had with UFO.