Symptoms

Error encountered when trying to use K2 in SharePoint as App
 

Diagnoses

The following error occurs when trying clicking on the K2 ribbon to applify a list.

SmartObject Server Exception: Error refreshing Service Instance '****************'. Service returned : 'System error.Failed to initialize the Context: URL: https://**************/******* Username: Error Details: Method: SharePointService.initializeContext '.

This has been working fine upto now, so this appears to be a new problem.
 

Resolution

To get around the error you will nee to refresh the service instance that is being referenced within the error itself from the smart object tester tool.

This should resolve the issue at hand.