the event suggest "registration rejected' so to me the provisioning must be fine.
jabber registration has three steps.
1) subscribe for provisoning
2) VCS send notify with provisioning
3) movi/jabber sends Register message.
since the login is failing at the REGISTER message i believe the provisioning must be fine. anyways as other said pulling logs would be easy of confirming that.
i am assuming that you have traversal setup working fine and authenticating the users using vcs control database. in this scenario the actual user is not available in the vcs-exp.
can you try to see if your "default subzone" is set to 'check credential"? if yes, can you change it to "treat as authenticated" for testing purpose and share the result.