After you reinstalled the game, did the game become unregistered? If not, then there must be some traces(settings, saved games, registration information, etc.) somewhere left on your computer, which, I think, is very likely the cause of the problem.
What Randomizer said was right, deleting files from the installation folder will cause errors. While I think it safe to delete corrupted settings and saves that outside the installation folder. The game will automatically regenerate these files the next time you run it anyway.
I suggest you make a backup first, then delete the entire folder called Avadon Saved Games(Not sure about its exact location since it differs between systems. Do a file search.), reinstall and run the game, re-register and tune up, then start over like what I did on a new computer. This eradicates all possible corrupted files.