You have Cerberus setup on a non domain server and are trying to access a remote resource via UNC path.
Create a local account on the destination server (domain server) to mirror a local account on the host server (non domain joined server in the DMZ)
Set the Cerberus service to use above account
Modify the host file on the non-domain joined host server to utilize common name to resolve IP address of destination server
Connect in Cerberus using common name (UNC path)