Symptoms

When attempting to use the "Batch Action" option (even on a single one) the popup screen was stuck on "Loading...". There was a "Permission denied" error in IE's F12 debugger functionality, and there was an item in the log that may be related.

"1552659"
"2015-03-09 11:42:56"
"Error"
"General"
"1"
"GeneralErrorMessage"
"SharePointProvider.GetGroupContainers"
"1 An unexpected failure was encountered when contacting SharePoint to get information from the group provider Cineplex Central: K2 Server does not have the necessary permissions on the SharePoint server or cannot authenticate with the server.

InnerException: The request failed with HTTP status 401: Unauthorized."

"HOSPAPP01:C:Program Files (x86)K2 blackpearlHost ServerBin"
"1552659"
"a647d20585c24018bc4fda58c53dc117"
 

Diagnoses

The problem was occurring because the worklist web part was being displayed in an iFrame. A seamless experience between SharePoint 2010 Site Collections and SharePoint 2013 was planned. But the web part uses native modal dialog and there seemed to be some bug in the code when using iFrames.
 

Resolution

Using an iFrame on the workspaces worklist fixes the problem.