Send package from Arduino to Xbee in API Mode

I've the following scenario: One Xbee Series 1 (coordinator) connected to the computer through Xbee USB xplorer and using the XCTU software in API mode (AP=2), and another Xbee Series 1 (end device) connected to an Arduino UNO through a Shield (also configured in API mode). Both are in the same PAN ID and can send and receive text messages in AT mode. I can send an API frame from XCTU to the Xbee connected to Arduino and I get a response. Now I'm trying to program arduino's code to send a remote at commands to the coordinator but it's not working. Here you can see the code I'm using:

#include <XBee.h>
#include <SoftwareSerial.h>

SoftwareSerial ss(3,2); //RX, TX
XBee xbee = XBee();

uint8_t atCmd[] = {'M','Y'}; //command AT
uint8_t atVal[]={}; // command AT value

XBeeAddress64 remoteAddress = XBeeAddress64(0x0013a200, 0x40cc0b20);
RemoteAtCommandRequest remoteAtRequest = RemoteAtCommandRequest(remoteAddress, atCmd);
RemoteAtCommandResponse remoteAtResponse = RemoteAtCommandResponse();

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  xbee.begin(Serial);
  ss.begin(9600);
  delay(5000);

}

void loop() {
  // put your main code here, to run repeatedly:
  sendRemoteAtCommand();
  remoteAtRequest.clearCommandValue();
}

void sendRemoteAtCommand() {
  ss.println("Sending Command");
  xbee.send(remoteAtRequest);

  if(xbee.readPacket(5000)){
    if(xbee.getResponse().getApiId() == REMOTE_AT_COMMAND_RESPONSE) {
      xbee.getResponse().getRemoteAtCommandResponse(remoteAtResponse);
      if(remoteAtResponse.isOk()){
        ss.print("Command [");
        ss.print(remoteAtResponse.getCommand()[0]);
        ss.print(remoteAtResponse.getCommand()[1]);
        ss.print("] was successful");

        if(remoteAtResponse.getValueLength() > 0){
          ss.print("Command value length is ");
          ss.println(remoteAtResponse.getValueLength(), DEC);
          ss.print("Command value: ");

          for(int i = 0; i < remoteAtResponse.getValueLength(); i++){
            ss.print(remoteAtResponse.getValue()[i], HEX);
            ss.print(" ");
          }
          ss.print(" ");
        }
      } else {
        ss.print("Command returned error code: ");
        ss.println(remoteAtResponse.getStatus(), HEX);
      }
    } else {
      ss.print("Expected Remote AT response but got ");
      ss.println(xbee.getResponse().getApiId(), HEX);
    }
  } else if (xbee.getResponse().isError()){
    ss.print("Error reading packet. Error code: ");
    ss.println(xbee.getResponse().getErrorCode());
  }else{
    ss.print("No response from radio");
  }
}

I'm just trying to send the command ATMY and get the response from the coordinator, but what I get is the "No response from radio".

Here is the example (and library) I'm using https://code.google.com/p/xbee-arduino/source/browse/examples/RemoteAtCommand/RemoteAtCommand.pde It's the same but with a diferent request.

Anyone have some idea about what can be wrong?

Thank you!!