I ran into this error message yesterday SEVERAL times while trying to install Canola2 on my N800 with OS2007. I ended up disabling ALL the repositories in the Application catalog EXCEPT for the following 3:
-Nokia Catalogue,
-http://repository.maemo.org bora free non-free
-http://repository.maemo.org/extras bora free non-free

In addition, I was in Red Pill mode.

This may be too limiting for some folks (as far as what you can install), but it helped me with Canola2.

Otherwise, I would think that the repositories are still screwed up...