I some times (around 3 of 100 registrations fails) gets the exception: System.Threading.ThreadAbortException: Thread was being aborted. at System.String.GetHashCode() at System.Collections.Hashtable.GetHash(Object key) at System.Collections.Hashtable.get_Item(Object key) at System.Data.DataColumnCollection.get_Item(String name) at System.Data.DataRow.get_Item(String columnName) at EPiServer.DataAbstraction.GroupSid.SaveGroupMembership() at EPiServer.DataAbstraction.GroupSid.Save() when trying to run this code: GroupSid groupSid = GroupSid.Load ("XXXGroup"); UserId userId = null; try { UserSid userSid = new UserSid (SecurityIdentityType.ExtranetUser); userSid.Name = name; userSid.Password = password; userSid.Active = true; userSid.Save (); userId = new UserId (userSid.ID); groupSid.GroupMembers.Add (userSid); groupSid.Save (); } catch (Exception ex) { .... } Can someone please give me some ideas on why the Save method throws this exception?