If you have problem trying to backup your ROM using CWM with snag, like „can’t mount mtdblock5” (-logfile) or just „Can’t mount /data”… try to run Fix Premissions from Rom Manager App. It works quite different than „Fix premissions” from CWM. That helped me.
I also tried updating CWM or disabling ExtROM in HBOOT in my HTC HD2 with no success before above solution.