Symptoms

K2 is logging errors along the line "Failed to resolve 'SP::GROUP PROVIDER]]GROUP]': An unexpected failure was encountered when contacting SharePoint to get information from the group provider GROUP PROVIDER]: Server was unable to process request. ---> Object reference not set to an instance of an object.
 

Diagnoses

Locate the entry for the group provider in the K2.HostServer.GroupProvider table and verify that the associated URL is valid.
 

Resolution

If the URL is invalid, removing the entry for the Group Provider from the table will resolve the error.