Why would rosserial_python fail when it connect to arduino?

edit

Hi! I running in 14.04 indigo, I need a hand to fix this problem :

I followed the tutorial of arduino in ros , try to create a publisher but it failed

$rosrun rosserial_python serial_node.py /dev/ttyACM0

[ERROR] [WallTime: 1509590980.692109] Creation of publisher failed: line: yaml https://raw.githubusercontent.com/ros... osx unsupported pickle protocol: 4

I tried to use $rosdep update to fix but nothing happend

Arduino code is here:

#include <SPI.h>
#include <MFRC522.h>

/////setup/////
#include <ros.h>
#include <std_msgs/String.h>
#include <std_msgs/Byte.h>
#include <std_msgs/Char.h>
#include <std_msgs/Int32.h>


ros::NodeHandle  nh;
std_msgs::String str_msg;
ros::Publisher chatter("RFID", &str_msg);
char hello[13] = "hello world!";
char RFID[32];

////////////////


constexpr uint8_t RST_PIN = 9;     // Configurable, see typical pin layout above
constexpr uint8_t SS_PIN = 10;     // Configurable, see typical pin layout above

MFRC522 rfid(SS_PIN, RST_PIN); // Instance of the class

MFRC522::MIFARE_Key key; 

// Init array that will store new NUID 
byte nuidPICC[4];

void setup() 
{ 
  //////node setup///////
  nh.initNode();
  nh.advertise(chatter);
  /////////////

  SPI.begin(); // Init SPI bus
  rfid.PCD_Init(); // Init MFRC522 

  for (byte i = 0; i < 6; i++) {
    key.keyByte[i] = 0xFF;
  }


void loop() 
{
  /////////ROS setup/////////
  //str_msg.data = RFID;
  //chatter.publish( &str_msg );
  nh.spinOnce();
  //delay(1000);
  ///////////////////////////


  // Look for new cards
  if ( ! rfid.PICC_IsNewCardPresent())
    return;

  // Verify if the NUID has been readed
  if ( ! rfid.PICC_ReadCardSerial())
    return;

  if (rfid.uid.uidByte[0] != nuidPICC[0] || 
    rfid.uid.uidByte[1] != nuidPICC[1] || 
    rfid.uid.uidByte[2] != nuidPICC[2] || 
    rfid.uid.uidByte[3] != nuidPICC[3] ) {

    nh.loginfo("A new card has been detected.");
    nh.loginfo("The NUID tag is:");


    sprintf(RFID,"%d %d %d %d",rfid.uid.uidByte[0],rfid.uid.uidByte[1],rfid.uid.uidByte[2],rfid.uid.uidByte[3]);
    str_msg.data = RFID;

    //show data
    nh.loginfo(RFID);
    chatter.publish( &str_msg );
    // Store NUID into nuidPICC array
    for (byte i = 0; i < 4; i++) {
      nuidPICC[i] = rfid.uid.uidByte[i];
    }  
  }
  else 
  nh.loginfo("Card read previously.");   
  // Halt PICC
  rfid.PICC_HaltA();   
  // Stop encryption on PCD
  rfid.PCD_StopCrypto1();
}

And my launch file is here

<launch>
  <node pkg="rosserial_python" type="serial_node.py" name="serial_node" output="screen">
    <param name="port" value="/dev/ttyACM0"/>
    <param name="baud" value="57600"/>
  </node>
</launch>

But I run these script on the other computer it's doesn't happened...

Can somebody help me?