I've had this issue with other apps. Problem is I can't remember how I remedied it. (1) 1st, try restarting yor computer. (2) Repair permissions if that doen't work. (3) Uninstall & try again!
In OS9 you could rebuild your desktop & in many cases everything would be hunky-dory. But in OSX, it's not so simple despite the problem is probably somehow related. I do know that a week/so after this happened the app would mysteriously open fine.