As SRK said, you "should" flash your Roms through your Recovery, and not through Rom Manager. The thread on the site, was more than likely written some time ago, and probably only successful on a smidgen of phones at the time.
The benefits of Rom Manager, are that it allows an easy method of, Backups, Management of backups, Flashing perhaps a new version of Clockwork recovery, Checking for newer versions of Roms for your device and downloading them. But nowdays, it's highly advisable to flash through your recovery menu.
Nuff said.