qz.exception.NullPrintServiceE...

function printopbill() {
          if ($('[id*="txtBillNo"]').val() != "") {
          document.getElementById('<%=HiddenField4.ClientID %>').value = 0;
         // qz.append("\x1B\x40"); // 1
        //  qz.append("\x1B\x21\x08"); // 2

          qz.append("                       45465465                           \r\n");
          qz.append("            48878787              \r\n");
          qz.append("                        45454545                                \r\n");
          qz.append(" OP REGISTRATION \r\n");
          qz.append("----------------------------------------------------------------------------\r\n");

          qz.append("Bill No    :" + $('[id*="txtBillNo"]').val() + "    Date:" + $('[id*="txtBillDate"]').val() + " \r\n");
          qz.append("OP No      :" + $('[id*="txtFileNo"]').val() + "\r\n");
          qz.append("Patient    :" + $('[id*="txtFirstName"]').val() + "                       \r\n");
          qz.append("Doctor     :" + $('[id*="ddlDoctor"]').find(":selected").text() + " \r\n");
          qz.append("----------------------------------------------------------------------------\r\n");
          qz.append("|Sl NO   |Particulars                                  |AMount            \r\n");
          qz.append("----------------------------------------------------------------------------\r\n");
          qz.append("|   1    |Registration Charge                          |" + $('[id*="txt_RegstnFee"]').val() + "\r\n");
          qz.append("|   2    |Consultation fee                             |" + $('[id*="txt_ConsultationFeeS"]').val() + "\r\n");
          qz.append("----------------------------------------------------------------------------\r\n");
          qz.append("                                        Total amount     :" + $('[id*="txtPatientTotal"]').val() + "\r\n");
          qz.append("                                        Round off        :" + $('[id*="txtRoundOff"]').val() + "\r\n");
          qz.append("                                        Recived amount   :" + $('[id*="txtPatientReceived"]').val() + "\r\n");
          qz.append("                                        Balance          :" + $('[id*="txtPatientShareBalance"]').val() + "\r\n");
          qz.append("----------------------------------------------------------------------------\r\n");
          qz.append("\r\n");
          var param1 = new Date();
          var param2 = param1.getDate() + '/' + (param1.getMonth() + 1) + '/' + param1.getFullYear() + ' ' + param1.getHours() + ':' + param1.getMinutes() + ':' + param1.getSeconds();
          qz.append("End of report. Printed on" + param2 + " ,User:" + '<%= Session["UserName"] %>' + ".Medismart");
          qz.append("\x1B\x21\x01"); // 3
          qz.append(" \r\n");
          qz.append(" \r\n");
          qz.append(" \r\n");
          qz.append(" \r\n");
              qz.append(" \r\n");
              qz.append(" \r\n");
              qz.append(" \r\n");
              qz.append(" \r\n");
              qz.append(" \r\n");
              qz.append(" \r\n");
              qz.append(" \r\n");

          qz.append("\x1D\x56\x41"); // 4
          qz.append("\x1B\x40"); // 5

         // window.setTimeout(function () {
              // this will execute 1 second later

              printHTML();
              window.location.href = "OPBilling.aspx";
          //}, 1000);




          return true;
          }
          else {
              return false;
          }
      }

qz.exception.NullPrintServiceException: qz.PrintRaw.print() failed.