If you look through the logs, I am guessing that there is something about the vmail database failure... This is often due to the system being unable to lock the vmail database and get exclusive access to it, most likely because a port is in use or stuck. State all your VM ports and see if one is in use and busy it out then rts it and try again. In some cases you have to get into the rtc shell and issue iPVM_Stop and wait for confirmation, then iPVM_Start and wait for confirmation then try the backup again.
