Symptoms
Application Error : K2 for SharePoint failure to open
Diagnoses
K2 for SharePoint integration window fails to open on a SharePoint document library. Depending on the user either of the attached errors is returned.
Resolution
Problem was caused by the Silverlight Isolated Storeage Cache for that site getting corrupted on that specific Client Machine . Opened Silverlight and deleted the Isolated Storage cache for that site , opened it up again and it worked