I encountered an issue and I thought I share the solution. Maybe most of you already know.
Root cause: Config XML got stuck in Check Out state. Like a normal document in a document library.
Solved! Go to Solution.
I'm getting a similar error, but I can't access the URL to the Config XML and discard the check out using your method.
I am using 365 cloud. would it be any different to access the URL to the Config XML?