This was driving me absolutely nuts.
A helpful post pointed me at [C:\Windows\System32\Configuration], and get rid of the pending.mof file. But that didn’t help.
Then I found Test-DscConfiguration
… which then led me to this:
, and finally the answer – Remove-DscConfigurationDocument -Stage Pending
Now I had that, I could finally do the thing I wanted (content really doesn’t matter):
Now I can get on with the original goal.