I recently encountered (and resolved!) an error upgrading a machine to Fedora 7. I reasoned it was worth sharing, so here you go:

Early in the process, an Anaconda screen prompted me to decide between a full install (to overwrite the existing FC6) or an upgrade. After I chose "upgrade," the installer choked with this stack trace:

Traceback (most recent call first): File "/usr/lib/anaconda/iw/upgrade_bootloader_gui.py", line 78, in _newToLibata if l.strip()[0] == "#": File "/usr/lib/anaconda/iw/upgrade_bootloader_gui.py", line 90, in getScreen newToLibata = self._newToLibata(anaconda.rootPath) File "/usr/lib/anaconda/gui.py", line 1131, in setScreen new_screen = self.currentWindow.getScreen(anaconda) File "/usr/lib/anaconda/gui.py", line 1042, in nextClicked self.setScreen () IndexError: string index out of range

I dug deeper in the stack trace and found the culprit: Anaconda didn't like that the system's /etc/modprobe.conf began with comment lines. I removed those, restarted the upgrade, and it went off without a hitch.

Hopefully this will spare you a headache or two.