Symptoms

I receive "the operation could not be completed because the item was removed from gallery" when adding "K2 smartforms viewer" web part to a SharePoint 2010 site.
 

Diagnoses

K2 for SharePoint components were not installed on SharePoint App server.
Missing...
- K2 for SharePoint - K2 Designer smartforms Client Event.wsp
- K2 for SharePoint - smartforms Web Parts.wsp

 

Resolution

Running the smartforms setup.exe on the sharepoint app server alleviated the issue as two .wsps are downloaded and deployed while running of the smartforms setup.exe via sharepoint 2010 webparts selection.