How to update two lists using SPWeb

Question

I have custom master detail form (ASPX)..i want to update masterblock and detail block in one function. i am doing like the following but getting below mentioned error. How can I update two lists items in one function.

Sharepoint Error: Save Conflict Your changes conflict with those made concurrently by another user

Here's My code

public void UpdateGridItem(int reqID, int gridItemId, string itemqty, string itemneedby, string finalRemarks)
        {
            string camlQueryDetail = @"<Where><And><Eq><FieldRef Name='Title' /><Value Type='Text'>"+reqID+"</Value></Eq><Eq><FieldRef Name='Item_x0020_ID' /><Value Type='Number'>" +gridItemId +" </Value></Eq></And></Where>";
            string camlQueryMaster = @"<Where><Eq><FieldRef Name='Title' /><Value Type='Text'>" + reqID + "</Value></Eq></Where>";

            using (SPSite objSite = new SPSite(PortalUrl))
            {
                using (SPWeb objWeb = objSite.OpenWeb())
                {
                    objWeb.AllowUnsafeUpdates = true;

                    // Building a query
                    SPQuery query = new SPQuery();
                    SPQuery qMaster = new SPQuery();

                    query.Query = camlQueryDetail;
                    qMaster.Query = camlQueryMaster;

                    // Retrieving the data from the Detail List
                    SPList objList = objWeb.Lists["Requisition_Detail"];
                    SPListItemCollection items = objList.GetItems(query);

                    SPList objListMaster = objWeb.Lists["Requisition_Master"];
                    SPListItemCollection itemsMaster = objList.GetItems(qMaster);

                    SPListItem listItems = items[0];
                    SPListItem listItemsMaster = itemsMaster[0];

                    listItems["Quantity"] = Convert.ToInt32(itemqty);
                    listItems["Needed_By"] = itemneedby;
                    listItems.Update();

                    listItemsMaster["Header_Remarks"] = finalRemarks;                   
                    listItemsMaster.Update();

                    objWeb.AllowUnsafeUpdates = false;
                }
            }
        }

Answer 1

If the sequence is the problem, try to do this:

                // Retrieving the data from the Detail List, Edit, Update
                SPList objList = objWeb.Lists["Requisition_Detail"];
                SPListItemCollection items = objList.GetItems(query);
                SPListItem listItems = items[0];
                listItems["Quantity"] = Convert.ToInt32(itemqty);
                listItems["Needed_By"] = itemneedby;
                listItems.Update();

                // Retrieving the data from the Master List, Edit, Update
                SPList objListMaster = objWeb.Lists["Requisition_Master"];
                SPListItemCollection itemsMaster = objList.GetItems(qMaster);
                SPListItem listItemsMaster = itemsMaster[0];
                listItemsMaster["Header_Remarks"] = finalRemarks;                   
                listItemsMaster.Update();