If you're using Redhat 7.2, you have a few options to get to single-user. I think Redhat puts this stupid graphic selection screen in if you're using LILO. I can't remember exactly, but I think you can press ctrl+X to get to a text prompt. From there, you should be able to type:
linux single
to boot into single user. I'm not sure what to do if you installed grub instead.
If you can't do this, either use your boot disk (or rescue disk, if you created one) and at the prompt there, you can either type "linux single" (from resuce disk) or "linux single root=/dev/hda" (from regular boot disk, assuming /dev/hda is your root partition).
In most cases, by default, it will drop you into a root shell, where you can check the /etc/passwd and /etc/shadow file for the root account (the very top line). Look for anything odd in there, and post back to let us know what's going on.
Aside from this, all I can find on this particular error is that it's an obscure bug in GNU-fileutils. If the passwd file doesn't turn anything up, you may try recompiling and installing fileutils, the alpha (caution, test code!) of which can be found here:
ftp://alpha.gnu.org/gnu/fetish/
Good luck!