Symptoms
Does K2 4.6.11 support Microsoft .NET 4.6.1?
Diagnoses
After inspecting the Blackpearl Support Matrix page (here: http://help.k2.com/blackpearl/support-matrix_NET ) it seems implied that it should be supported.
Resolution
K2 Blackpearl 4.6.11 does NOT support Microsoft .NET 4.6.1 - it only supports .NET 4.6.0
I have logged a documentation request to update that page.