Symptoms

All our K2 applications which use method 'Get Users In Group' throw 401 error message. I've checked in SmartObject Service Tester tool that this method throws exception:

'The request failed with HTTP status 401: Unauthorized.
Service: SharePointGroupsService
..

Error 401 occurs both K2 service account and regular users. K2 servcie account is site collection administrator. This was working before but suddenly stopped. We don't know what the reason could be as we have not done any K2 reconfiguration.

We have the same configuration for Stage environment where it works.
 

Diagnoses

Possible proxy error
 

Resolution

Confirmed that the issue was indeed caused by a proxy server that wasn't configured correctly.