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This may not be related, but on ONE install (I've been through a couple of clean installs due to disk problems), I found that in the course of moving and reinstalling stuff, the system forgot that I was an administrator. Really annoying, and I hated the idea of starting all over. So I did some investigation and hacked my way back in. The easiest way I could think of to recover was to set a root password from the install CD, then use NetInfo (with the root password to allow access, which worked even though the root account hadn't actually been enabled for login... though I ended up doing that, too) to add my account back into the 'admin' group. (From which it had been removed.)