Wavelab Pro 9 unexpectedly quit while reopening windows

Reinstalling the app doesn’t usually solve the problem, because usually this happens from a corrupt preferences file.

PG might be able to tell you precisely which one (usually General.dat) but the sure way is to delete the entire preferences folder. You of course lose all settings but if you back up the folder first to another location, you can also put back some preferences hopefully without corrupting things again.