Hi n900 folks. Been trying to partition my 8 gb SD card, following instructions at http://wiki.nitdroid.com/index.php?title=N900-install. However, I get stuck at unmount with a message that says:

umount: cannot umount /dev/mmcblk1p1: invalid argument

Could someone please help me get past this stage? I have tried everything I know (not much) and it still gives me the same message.