I've been fighting with this same issue since yesterday. it is specifically the http://repository.maemo.org/ repo causing the problems. and that goes for pretty much all fields. I just reflashed my n800 and did not restore my backup so everything was completely fresh. using the maemo garage install links i still could not install kagu. I'm contemplating reflashing with the beta just to see if its the repo or a bad release.

As of now I'm regretting doing the reflash since nothing is installable.