A little bit of further info..

Turning on object fail auditing gives rise to event 4656:

Object:

Object Server:SC Manager

Object Type:SC_MANAGER OBJECT

Object Name:ServicesActive

Handle ID:0x0

Process Information:

Process ID:0x208

Process Name:C:\Windows\System32\services.exe

Access Request Information:

Transaction ID:{00000000-0000-0000-0000-000000000000}

Accesses:Connect to service controller

Enumerate services

Access Reasons:-

Access Mask:0x5

Privileges Used for Access Check:-

Restricted SID Count:0

This seems to imply that there's a failure to access the service controller to enumerate the object. It's strange that this should occur on a connection from the SQL job (that's meant to be local, and responds as such) and not a SQLPS, or even a SQLPS initiated from the management studio that's supposed to operate in the same context.

I'll kick this around as soon as I get time, unless anyone's come up with an answer they're willing to share. I suspect it's going to mean editing the auth strings for the SCM.