[Luccia at Pelican Parts]

Did you look at these threads:

http://forums.pelicanparts.com/mini-discussion-forum/996330-all4-countryman-2c57-code.html
http://forums.pelicanparts.com/mini-discussion-forum/996330-all4-countryman-2c57-code.html
http://forums.pelicanparts.com/mini-discussion-forum/945879-question-turbocharger-wastegate-testing.html

I know you said you've tested the wastegate, but just in case make sure you've looked over this tech article: https://www.pelicanparts.com/techarticles/MINI_R56/139-EXHAUST-Turbocharger_Wastegate_Testing/139-EXHAUST-Turbocharger_Wastegate_Testing.htm.