In the process of munging our RHEL5 kickstarts to RHEL6, we started getting this error "Partition requires a size specification", the partition had a size of 0 set in the kickstart, with grow.
reading kickstart.py, it seems that the check for size has gone from pd.size = None to not self.size
part pv.2 --size=0 --grow
The fix was simple enough then, just change size from 0 to 1.
if not self.size and not self.onPart: raise KickstartValueError, formatErrorMsg(self.lineno, msg="Partition requires a size specification")
part pv.2 --size=1 --grow