Originally Posted by zszabo

If you don't want to do a reflash, consider forcing a re-install of the original Nokia packages ("apt-get --reinstall install ..." -- of course this can be problematic when packages were incepted and have a higher security priority than the ones supplied by Nokia; in that situation, you can probably still download them by using -d and then re-incepting them).

Using this technique, I've managed to fix an N900 repeatedly that was otherwise hopelessly screwed up; just make sure root access via ssh is always one of the first things you enable on the phone. With the right configuration, you can sometimes even fix the phone when the UI is completely broken (this doesn't apply as much to the N9 of course, due to MALF).

As for which packages need to be re-installed -- I have never been systematic enough to create a specific list, but usually found the culprits by re-installing packages that seemed UI-related. You can also often find out all related package names with a search query like "apt-cache showpkg <package-name>".

The downside of this procedure is that all customizations are lost (but then again, that is often the cause of your problems to begin with).