1 – you have a rscd on your psexec helper and psexec is in system32?
2 – your role can talk to the psexec helper properly (watch the rscd on the helper when you run the job)
3 – admin$/c$ are open on the target?
Not sure about the ‘host null’ message though.
Check which authentication rule is getting used for this server IP.
Check if the rule which is used to authenticate this machine is correct.