Tapes involved in your setup?
Preferably, you need to have your VM backups, go to disks and not overflow to a tape pool. If you have tapes involved, the "control files" needed to do the subsequent backups need to be read from tape. If you do not have enough drives and/or they are all taken and/or tape is used by something else, your VM backup will fail with that error. Best bet is, if you do have "tapes" involved in your setup is to have a dedicated disk pool for your control files, and you can us the VMCTLmc option in your opt file to point all your control files to.
If no tapes involved and/or all volumes are online, have you tried to force a full backup of your VM to recreate the control file?