From what I've read, this code is supposed to fetch all WorklistItem from a K2 process. Problem is that it only retrieves those assigned to the current authenticated user.
WorklistCriteria wlc = new WorklistCriteria();
wlc.AddFilterField(WCField.ProcessID, WCCompare.Equal, ProcessInstaceId);
return connection.OpenWorklist(wlc);
Connection is set through windows authentication and integrated security. Would there be a parameter to tweak in order to get all WorklistItem no matter who they are assigned to ?