Rosserial multiple publishers

edit

I'm running a fresh install of Ubuntu 13.04, rosserial, hydro.

Using an arduino uno, the following code works and publishes messages:

#include <ros.h>
#include <std_msgs/Int16.h>

ros::NodeHandle nh;
std_msgs::Int16 ultrasound_msg;
std_msgs::Int16 ir_msg;
ros::Publisher ultrasound_pub("ultrasound", &ultrasound_msg);
ros::Publisher infrared_pub("infrared", &ir_msg);


void setup() {
  // Initialize sensors, etc
    nh.initNode();
    nh.advertise(ultrasound_pub);
    //nh.advertise(infrared_pub);
}

void loop() {

  ultrasound_msg.data = 42;
  ultrasound_pub.publish( &ultrasound_msg );

  nh.spinOnce();
  delay(1000);

}

If I un-comment the second advertise:

void setup() {
  // Initialize sensors, etc
    nh.initNode();
    nh.advertise(ultrasound_pub);
    nh.advertise(infrared_pub);
}

I get 'Creation of publisher failed: unpack requires a string argument of length 4', when I try to start the node on the ROS side.

When I try to initialize only the second publisher:

void setup() {
  // Initialize sensors, etc
    nh.initNode();
    //nh.advertise(ultrasound_pub);
    nh.advertise(infrared_pub);
}

Starting the node says 'Unable to sync with device; possible link problem or link software version mismatch such as hydro rosserial_python with groovy Arduino'

I saw 2 posts with similar problems, solved by updating the rosserial-arduino and rosserial installations. I have fresh installations from apt-get, so I'm not sure why they'd be mismatched.

Any ideas?

UPDATE

If I replace the second publisher with a subscriber like so:

void ROS_CALLBACK(const std_msgs::Int16 &msg)
{
  // do stuff
}
ros::Publisher ultrasound_pub("ultrasound", &ultrasound_msg);
ros::Subscriber<std_msgs::Int16> sub("arduino_listener", &ROS_CALLBACK);
...
void setup() {
  // Initialize sensors, etc
    nh.initNode();
    nh.advertise(ultrasound_pub);
    nh.subscribe(sub);
}

I get the same errors for the same sequence. 'Failed to unpack' for the code shown below. 'Unable to sync with device' if I advertise subscribe without advertising the publisher.