Generally, if prefs can be fixed but then go bad again, it's best to trash the app, making sure that you also trash prefs, and reinstall.
You can spend the rest of time trying to fix it and you might get lucky, but the few minutes it takes to reinstall, will make things easier.
Using OSX 10.3.9 & 10.4.11 on a G4, G5 & Intel Macbook