Thanks Jawahar. That got rid of the email problem.
Now I get:
Commit Status=Commit attempted and failed., Promotion Status=Failure : Delivery results to destination (CrystalEnterprise.DiskUnmanaged) failed.
: (
But that is a separate problem to the one I had so I've marked you as providing the Correct Answer.
Cheers.
Edit: Finally solved it. First thing, is the rexec service needs to be running on *nix (part of RSH). This is an insecure and superseded protocol so a lot of modern systems won't have it turned on -- you may have to convince your sysadmins.
Second, the directory address doesn't need the UNC format (ie //servername/directory ) in *nix in order to work. In fact it won't work with it.