Symptoms

Getting error message "Thread 1: Object Reference not set to an instance of an object" when trying to open the K2 Application page on any of the lists/libraries.

 

Diagnoses

K2 Application was failing at the SharePoint Integration Helper SmartObject (method name="GetK2ForSharePointFormDetails).
When comparing the results to a succeeded ajax call below, the response didn't containt Smartforms Designer URL. Next, we checked Smartforms Designer SSL environment Library field and found that it was missing.

true5a173365-d13c-4a12-a7e4-7fb877e54c8920197falseDenallix SiteDocumentsShared DocumentstruetrueDocuments Workflowhttps://k2.denallix.com/DesignerTrueProtection Action,Protection Tag,Protection Tag Modified,ID of the User who has the Set the Protection Tag,Record,Shortcut Site Id,Shortcut Web Id,Shortcut Unique IdreadGetK2ForSharePointFormDetailsCapture
 

Resolution

Some high level steps would be:
-Make sure the Smartforms Designer SSL is in Environment Fields and it?s set to True value.
-Navigate back to the app catalog. Re-run the K2 for SharePoint Registration wizards.
-Go back to the library and confirm K2 application is working.