The bug affecting DiskAid preventing it to access Root folder under “jailbroken” OS 3.1.2 is due to a missing config patch in a config file within “Blackra1n”.
You can fix that by downloading the “afc2add” from Cydia!
For your info also, the Dev Team has come to jailbreak 3.1.2 too, and no problem has been reported so far! More info : http://blog.iphone-dev.org
PLEASE NOTE: DigiDNA does not encourage nor supports “jailbreaking” or any other means and/or attempts to reverse engineer any Apple software and/or device.