If the --onpart option is used with kickstart on the partition command,
anaconda dies in todo.py at line 395 at the line:
self.mounts[location] = (device, fsystem, reformat)
in the addMount method because mounts is not an attribute of self.
the --onpart option is known to have issues in 6.2 ... Red Hat Linux 7 has much
more robust behavior for this command ... please let me know if you are still
having this problem using 7 ... thanks for your report!
additionally, if this continues to be a problem for you please feel free to
attach the kickstart file, we'd be glad to try to verify any problems you have