pretty sure this:
http://talk.maemo.org/showthread.php?t=38872
or this:
http://talk.maemo.org/showthread.php...&highlight=.qf
will contain answers for most issues.

I also seem to remember that if your local install is missing files/folders for any reason, you can just delete it entirely and it will be recreated (without any cached/downloaded data, naturally) when you next run Ovi maps. That may help get you to a clean starting point? But I just downloaded map loader, connected n900 in USNB mode, and then followed the on-screen prompts, no need for any messing with .qf (or anything else).