Ressurrected this thread as I am having exactly this problem. Did anyone ever find a solution for it?

So...I flashed my N800 with the latest build. I try to install things but they all involve a adding an application catalogue and the application manager fails with a "failed to fetch 1.0.0.0" message.

Checked the proxy settings and I have no proxy enabled. My wireless is set to auto DNS and DHCP. I can browse but not connect to application catalogues. I've disabled all the catalogues I can but the nokia one which cannot be disabled. So I can't install anything at the moment.