Installer fails with exception after choosing upgrade from existing FC4 system.
Whole exception text is attached

Traceback (most recent call last):
  File "/usr/lib/anaconda/gui.py", line 951, in nextClicked
    self.dispatch.gotoNext()
  File "/usr/lib/anaconda/dispatch.py", line 146, in gotoNext
    self.moveStep()
  File "/usr/lib/anaconda/dispatch.py", line 217, in moveStep
    rc = apply(func, self.bindArgs(args))
  File "/usr/lib/anaconda/upgrade.py", line 273, in upgradeMountFilesystems
    allowDirty = 0)
  File "/usr/lib/anaconda/upgrade.py", line 147, in mountRootPartition
    oldfsset.mountFilesystems(instPath, readOnly = readOnly)
  File "/usr/lib/anaconda/fsset.py", line 1637, in mountFilesystems
    entry.mount(instPath, readOnly = readOnly)
  File "/usr/lib/anaconda/fsset.py", line 1840, in mount
    BindMountDevice))
  File "/usr/lib/anaconda/fsset.py", line 1050, in mount
    raise SystemError (errNum, errMsg)
UnboundLocalError: local variable 'errNum' referenced before assignment

Local variables in innermost frame:
device: /dev/hda1
bindMount: False
readOnly: 0
self: <fsset.AutoFileSystem instance at 0xb7dade6c>
mountpoint: /mnt/sysimage//mnt/diskc