I noticed this problem only a few days ago, so an actual time frame in which this happened is impossible to tell. I only noticed when our power went out and I went to go on the internet on my laptop with my phone's tether. I attempted to activate the tether and it told me I was not rooted, but the superusers app still appeared in my app directory. Whenever I clicked on the Superuser app it came up with a white screen that did not respond in any way other then to exit out of the app.
At first I simply attempted to re-root my phone via Z4root, downloading it directly to my phone and running it. The first time it seemed like it worked; the rooting proceeded as normal and restarted the phone, but I was still not rooted. The next time I attempted to root it using the same z4root app, the application crashed immediately when I told it to do a permanent root. I then attempted a factory reset, but it did not remove the superuser app. The same problem persisted with the z4root after that as well. Terminal Emulator does not work as I am obviously still not rooted, and the attempt to update my superuser app through Titanium Backup's 'problem?' menu gave me the error 'package file was not signed correctly.' I, of course, have no clue what that means.
So what need I do to fix this and get my phone rooted again? Is there any way to erase the entire thing including the superuser app? At this point I don't care if it's gonig to take a little while to fix.
I'm using a Droid 2, by the way. Any other information I can provide upon your asking.