How to solve database cuncurrency problem?

mConn = new OdbcConnection();
       mConn.ConnectionString = Global.mconnectionstr;
       mConn.Open();
       mTrans = mConn.BeginTransaction(IsolationLevel.Serializable);
       string mkey = "000000" + lib.FnGenAutoCode("MR", "RECURR", "PAY", 6, mTrans, (string)Session["COMPANYID"].ToString(), Session["BRANCHID"].ToString());
       MONEY_RECEIPT = "MR/" + mkey.Substring(Convert.ToInt16(mkey.Length - 6), (Convert.ToInt16(mkey.Length) - Convert.ToInt16(mkey.Length - 6)));
       if (ReadGrid())
       {
           int key = lib.FnGenAutoCode("TRN_COMMISSION_PAID", "TRN_COMMISSION_PAID", "TRN_COMMISSION_PAID", 5, mTrans, (string)Session["COMPANYID"].ToString(), Session["BRANCHID"].ToString());
           string fStrSql = " INSERT INTO [TRN_COMMISSION_PAID] VALUES (" +
          " '" + (string)Session["COMPANYID"].ToString() + "','" + Session["BRANCHID"].ToString() + "','" + key + "','" + adv_code + "','" + txtTotal.Text + "','" + DateTime.Now.Date.ToString("MM/dd/yyyy") + "'" +
          ",'" + MONEY_RECEIPT + "','" + tds_amt.ToString() + "','" + serv_amt.ToString() + "','" + project_amt.ToString() + "'" +
          " ,'" + payable_amt + "','" + Session["User"].ToString() + "','" + DateTime.Now.Date.ToString("MM/dd/yyyy") + "','','','I','" + txtLoan.Text + "')";
           if (lib.FnExecuteQuery(fStrSql, mTrans) && UpdateLoanAmount())
           {
               UserMsg = "Data saved successfully";
               lblstatus.Text = UserMsg;
               //PendingInstallMent(txtAdvisor.Text);
               clerfld();
               mTrans.Commit();
               string sql_adv = "select CODE from TRN_ADVISOR where REFCODE='" + txtAdvisor.Text + "'";
               string adv = lib.FnFetchText(sql_adv);

               Response.Write("<script>");
               Response.Write("window.open('CommissionVoucher.aspx?moneyreceipt=" + MONEY_RECEIPT +
                   "&adv=" + adv +
                   "&frmdate=" + lib.FnQuatationRps(txtFrmDate.Text) +
                   "&todate=" + lib.FnQuatationRps(txtToDate.Text) + "','_blank')");
               Response.Write("</script>");
           }
           else
           {
               lblstatus.Text = "Unable to Save record";
               mTrans.Rollback();
           }
           mTrans.Dispose();
           mConn.Close();
       }
       mTrans.Dispose();
       mConn.Close();