This problem drives me crazy. Here's the code

            using (BizNetDB db = new BizNetDB())
        {
            var dbServiceCall = db.ServiceCalls.SingleOrDefault(x => x.ServiceCallID == serviceCallDetail.ServiceCallID);
            var dbServiceCallDetail = dbServiceCall.ServiceCallDetaills.SingleOrDefault(x=> x.ServiceCallDetailID == serviceCallDetail.ServiceCallDetailID);

            if (dbServiceCallDetail == null)
            {
                dbServiceCallDetail = new Data.ServiceCallDetaill();
                dbServiceCall.ServiceCallDetaills.Add(dbServiceCallDetail);
            }

            dbServiceCallDetail.EndSession = serviceCallDetail.EndSession;
            dbServiceCallDetail.ExitTime = serviceCallDetail.ExitTime;
            dbServiceCallDetail.Solution = serviceCallDetail.Solution;
            dbServiceCallDetail.StartSession = serviceCallDetail.StartSession;



            serviceCallDetail.SessionMinutes = (serviceCallDetail.EndSession - serviceCallDetail.StartSession).Minutes;
            serviceCallDetail.DriveMinutes = serviceCallDetail.ExitTime.HasValue ? (serviceCallDetail.StartSession - serviceCallDetail.ExitTime.Value).Minutes : 0;

            var totalMinutes = (from d in db.ServiceCallDetaills
                                    .Where(x => x.ServiceCallID == serviceCallDetail.ServiceCallID && x.ServiceCallDetailID != dbServiceCallDetail.ServiceCallDetailID)
                        group d by d.ServiceCallID into g
                        select new { SessionMinutes = g.Sum(x => x.SessionMinutes), DriveMinutes = g.Sum(x => x.DriveMinutes) }).First();

            dbServiceCall.SessionMinutes = totalMinutes.SessionMinutes + serviceCallDetail.SessionMinutes;
            dbServiceCall.DriveMinutes = totalMinutes.DriveMinutes + serviceCallDetail.DriveMinutes;

            try
            {
                db.SubmitChanges();
            }
            catch (ChangeConflictException ex)
            {
                db.ChangeConflicts.ResolveAll(RefreshMode.OverwriteCurrentValues);
                db.SubmitChanges();
            }

The second Submit did solve the problem.. but I want to solve it from the root!

when I disabled this lines (The parent changes):

dbServiceCall.SessionMinutes = totalMinutes.SessionMinutes + serviceCallDetail.SessionMinutes;
        dbServiceCall.DriveMinutes = totalMinutes.DriveMinutes + serviceCallDetail.DriveMinutes;

everithing is Ok.

please help...