rosserial deserialization error

edit

I am trying to publish an odometry message from an arduino using rosserial. I have it publishing a tf message fine. But the odom message first required increasing the buffer_size and now gives this error:

[INFO] [WallTime: 1376950638.665497] ROS Serial Python Node
[INFO] [WallTime: 1376950638.671086] Connecting to /dev/ttyACM0 at 57600 baud
[INFO] [WallTime: 1376950641.232339] Note: publish buffer size is 1024 bytes
[INFO] [WallTime: 1376950641.232938] Setup publisher on tf [tf/tfMessage]
[INFO] [WallTime: 1376950641.242256] Setup publisher on odom [nav_msgs/Odometry]
Traceback (most recent call last):
  File ".../catkin_ws/src/rosserial/rosserial_python/nodes/serial_node.py", line 82, in <module>
    client.run()
  File ".../catkin_ws/install/lib/python2.7/dist-packages/rosserial_python/SerialClient.py", line 425, in run
    self.callbacks[topic_id](msg)
  File ".../catkin_ws/install/lib/python2.7/dist-packages/rosserial_python/SerialClient.py", line 99, in handlePacket
    m.deserialize(data)
  File "/opt/ros/groovy/lib/python2.7/dist-packages/nav_msgs/msg/_Odometry.py", line 220, in deserialize
    raise genpy.DeserializationError(e) #most likely buffer underfill
genpy.message.DeserializationError: unpack requires a string argument of length 288

Sometimes, about one in three, there is also this error right after the INFO messages shown above. I suspect it is just some sort of lost sync, since I just installed the latest version of rosserial on a new build of Groovy.

[ERROR] [WallTime: 1376951210.467803] Mismatched protocol version in packet: lost sync or rosserial_python is from different ros release than the rosserial client
[INFO] [WallTime: 1376951210.468270] Protocol version of client is Rev 0 (rosserial 0.4 and earlier), expected Rev 1 (rosserial 0.5+)

Here is the code:

/* 
 * rosserial Planar Odometry Example
 */

#include <ros.h>
#include <ros/time.h>
#include <tf/tf.h>
#include <tf/transform_broadcaster.h>
#include <nav_msgs/Odometry.h>

ros::NodeHandle  nh;

geometry_msgs::TransformStamped t;
tf::TransformBroadcaster broadcaster;
nav_msgs::Odometry myOdom;
ros::Publisher odom_pub("odom", &myOdom);

double x = 1.0;
double y = 0.0;
double theta = 1.57;

char base_link[] = "/base_link";
char odom[] = "/odom";

void setup()
{
  nh.initNode();
  broadcaster.init(nh);
  nh.advertise(odom_pub);
  myOdom.pose.covariance = {0.001, 0, 0, 0, 0, 0, // covariance on x
                        0, 0.001, 0, 0, 0, 0,  // covariance on y
                        0, 0, 0.001, 0, 0, 0,  // covariance on z
                        0, 0, 0, 99999, 0, 0,  // large covariance on rot x
                        0, 0, 0, 0, 99999, 0,  // large covariance on rot y
                        0, 0, 0, 0, 0, 0.001};  //covariance on rot z

}

void loop()
{  
  // drive in a circle
  double vx = 0.2, vy = 0.2;
  double vtheta = 0.18;
  x += cos(theta)*vx*0.1;
  y += sin(theta)*vy*0.1;
  theta += vtheta*0.1;
  if(theta > 3.14)
    theta=-3.14;

  /* 
  Serial.print("x , y, theta = ");
  Serial.print(x);
  Serial.print(", ");
  Serial.print(y);
  Serial.print(", ");
  Serial.println(theta);
  */

  // tf odom->base_link
  t.header.frame_id = odom;
  t.child_frame_id = base_link;

  t.transform.translation.x = x;
  t.transform.translation.y = y;

  t.transform.rotation = tf::createQuaternionFromYaw(theta);
  t.header.stamp = nh.now();

  broadcaster.sendTransform(t);
  nh.spinOnce();

  myOdom.header.stamp = nh.now();
  myOdom.header.frame_id ...