droid 2 root problems after gingerbread update

[xzero17x]

I recently rooted a friends phone using the superoneclick application on shortfuse.org after the update he came to me saying his phone no longer would run wireless tether. When trying to run the app it asks for super user permissions and if the phone is rooted although super user is still installed on the phone. I've tried deleting su and rooting. The phone won't unroot. I'm a little lost. Anybody know what to do from here?