Originally Posted by Matlock
NANDROID backups should be done from Manual Recovery (Either from ClockworkMod or Amon_RA). Not ROM Manager.
ROM Manager has been known to skip steps in it's own process.
So Boot into Recovery and perform all the process' manually.
Just my little addition to the PSA.
EDIT: Added thread to Guide. Just for kicks ^_^
I agree with you Matlock. To take it a step further ROM Manager is *okay* at first, especially if you're new to rooting and flashing. But all new rooters should get comfortable with navigating through recovery and doing things manually. Not only are you going to run into less problems with backups etc., you should get familiar with doing things manually anyway so you won't need to rely on something like ROM Manager.