How to start a BITS download as System Account? current error: "user has not logged on to the network" 0x800704DD

I'm trying to launch a BITS service download in a GPO Startup Script. Startup Scripts are started as the local SYSTEM account, which works well for background downloads as per Microsoft's documentation https://msdn.microsoft.com/en-us/library/windows/desktop/aa363152(v=vs.85).aspx

Sadly when I try to start a download (disregarding valid source or destination) I get the following error:

Start-BitsTransfer : The operation being requested was not performed because
the user has not logged on to the network. The specified service does not
exist. (Exception from HRESULT: 0x800704DD)
At line:1 char:1
+ Start-BitsTransfer -Source localhost -Destination c:\temp
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : NotSpecified: (:) [Start-BitsTransfer], COMException
+ FullyQualifiedErrorId : System.Runtime.InteropServices.COMException,Microsoft.BackgroundIntelligentTransfer.Management.NewBitsTransferCommand

This is just a test, the actual BITS transfer is started within a c# application that is launched within the GPO Startup Script. Further tests with a manually created process through Sysinternals PSExec yield the same error.

Additional checks for security principals in whoami /all look fine:

User Name           SID     
=================== ========
nt authority\system S-1-5-18

GROUP INFORMATION
-----------------

...
CONSOLE LOGON                          Well-known group S-1-2-1
...
LOCAL                                  Well-known group S-1-2-0
BUILTIN\Administrators                 Alias            S-1-5-32-544

I checked for services BITS and SENS - all running.

To summarize:

• How can i successfully launch a BITS download as SYSTEM in Startup Script?
• How does the error "user has not logged on to the network" make sense, considering System account is always logged on? What is the meaning of "The specified service does not exist." - what service?