Hi Karl,
One of the reason why this issue might appear is lack of privilege to SCOM Action Account User on the Windows Computer where the SCOM Management Server is running.
Please try and give additional privilege to SCOM Action Account User to that it could perform write operations to C:\Windows\Temp folder on the Management Server computer.
Or you can also try adding SCOM Action Account User to Local Administrators group...
Thanks,
Amit Kumar