Symptoms

New workflow is throwing an error "The request failed with HTTP status 401: Unauthorized." in the Admin portal of K2 blackpearl.

The event which is causing the failure is "Upload Request to Library" i.e. when the workflow tries to save the InfoPath form onto the form library after the user has submitted the new request.
 

Diagnoses

K2 Service account does not have sufficient rights.
 

Resolution

Add the K2 service account to the Site Collection Administrator group.