Symptoms

 Multiple errors in Windows Event Viewer on K2 server:

64005 Failed to resolve 'K2:DomainUserName': The specified account does not exist. Resolving User:DomainUserName.

64005 Failed to resolve 'K2:DomainGroupName': The specified account does not exist. Resolving User:DomainUserName.

 

Diagnoses

There are probably entries in the Identity.Identity table for which corresponding objects in AD DS were deleted. This could be related to SharePoint Group Providers registered in K2 Workspace or non-existing AD Users/Groups included in some Role.
 

Resolution 

Check Identity table in K2 database to verify if there are any enabled entries for users/groups that don't exist in AD DS anymore or any references to SharePoint Group Providers that didn't exist anymore.

At the moment there is no way to remove the erroneous/non-working SharePoing Group Providers directly in Workspace / Management Console GUI. This is designed so with idea that you have to remove the K2 features from the SP site in question first (before deleting site) and this process will remove group provider from K2. In scenario when SharePoint site had been already deleted but you still have corresponding group provider for it in K2 you had to remove the entries directly in oHostServer].eGroupProvider] table in the K2 DB.

WARNING: Always perform K2 database backup before making any changes in K2 DB. Any changes in K2 DB made without explicit instructions from K2 support may put you into unsupported state. Plese contact K2 support to get assistance with this operation.