Symptoms
K2 for SharePoint: AD FS
Diagnoses
The environment has been configured to use ADFS for SharePoint and for K2 successfully. At the moment it is not possible to access SharePoint 2013 SmartObjects from the SharePoint app or the K2 SmartObject Tester.
The error provided is "Operation is not valid due to the current state of the object."
This only happens when ADFS is used with the SharePoint Web Application.
Resolution
Making an upgrade to 4.6.9 and the issue should no longer persist after.