Me auto respondo.
He encontrado la solución buceando
If your sure there is nothing wrong with the backup, boot into recovery and do this:
use adb for this.
adb shell
You should now see ~ #:
Read the red, and change it.
replace <nameofbackup> with the folder your backup is in.
cd /sdcard/clockworkmod/backup/<nameofbackup>
rm -rf nandroid.md5
md5sum *img > nandroid.md5