If you try to compact (from inside the maemo mapper) the DB 'normally' it will tell if the DB file is corrupted. If you want to try it just go to menu, Maps, Manage Repositories.. , and press the button Compact...

But the proposal from Den should be a good quick try if your DB is the culprit. If you downloaded a lot you can just rename it (instead of deleting it) and later restore it.