then my next question is how can you run uname -a if you don't have developermode/terminal in your device. Sounds like that you might have added some non standard apt repositories in the device, like harmattan-dev or rzr (which are NOT nokia signed), which will conflict the default repo packages and will block installation of developer mode.

If you still have root console access, you could just reinstall the nokia signing keys, if keys are out of sync.