Digium phone can't forward calls

I have a Digium D50 connected to the latest stable Freepbx and every time the user tries to forward all calls to a different extension they get the error:

“Your account is not permitted to run this action: to_mailbox (27168)”

Anybody help me find where to start troubleshooting this?

I provisioned the phone with DPMA.

It seems that the extension the user was trying to forward to had no voicemail set up. I’m not sure how that’s related or where to look up those error codes.
But it’s working fine now. Thanks.