Rosserial checksum error

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When running "rosrun rosserial_python serial_node.py /dev/ttyACM0" I get the error message "wrong checksum for topic id and msg". After that it may continue to connect but the error "Serial Port read returned short (expected 78 bytes, received 5 instead)." comes up, or it may just not connect and keep trying. Whats weirder is if I restart the PC and run the code it works fine, I can launch RVIZ, with "roslaunch robot_description robot_description.py" and it will show me the range sensor and move about as i move my hand to and from the sensor. The next time I run it I get the above errors.

The code I am using is below. pretty basic for the tf stuff, really just copied the arduino copy as a test

//////////////////LIBRARIES///////////////////
#include <NewPing.h>
#include <ros.h>
#include <ros/time.h>
#include <sensor_msgs/Range.h>
#include <tf/transform_broadcaster.h>
//////////////////LIBRARIES///////////////////

//////////////////ROS Vars and OBJECTS///////////////////
ros::NodeHandle  nh;
sensor_msgs::Range range_msg;
ros::Publisher pub_range( "/ultrasound", &range_msg);
geometry_msgs::TransformStamped t;
tf::TransformBroadcaster sonar_broadcaster;

char base_link[] = "/base_link";  //set the TF child frame 
char odom[] = "/odom";
char frameid[] = "/ultrasound";
//////////////////ROS Vars and OBJECTS///////////////////


//////////////////SONAR Vars and OBJECT///////////////////
int sonar_pin =12;
NewPing sensor(sonar_pin, sonar_pin, 25);
//////////////////SONAR Vars and OBJECT///////////////////


void setup()
{
  nh.initNode();
  nh.advertise(pub_range);
  sonar_broadcaster.init(nh);


  t.header.frame_id =  frameid;
  t.child_frame_id = base_link;

  range_msg.radiation_type = sensor_msgs::Range::ULTRASOUND; //set the message type and the sensor radiation type
  range_msg.header.frame_id = frameid;
  range_msg.field_of_view = (10.0/180.0) * 3.14;
  range_msg.min_range = 0.0;
  range_msg.max_range = 10;


  digitalWrite(sonar_pin, HIGH); //turn internal pull-up resistor on
}

long range_time;

void loop()
{

  //publish the adc value every 50 milliseconds
  //since it takes that long for the sensor to stablize
  if ( millis() >= range_time )
  {

    t.header.frame_id = frameid;
    t.child_frame_id = base_link;
    t.transform.translation.x = 1.0; 
    t.transform.rotation.x = 0.0;
    t.transform.rotation.y = 0.0; 
    t.transform.rotation.z = 0.0; 
    t.transform.rotation.w = 1.0;  
    t.header.stamp = nh.now();
    sonar_broadcaster.sendTransform(t); 
    range_msg.range = sensor.ping_in();
    range_msg.header.stamp = nh.now();
    pub_range.publish(&range_msg);
    range_time =  millis() + 28;
  }

  nh.spinOnce();
}