Covariance/filter errors when launching robot_pose_ekf + iRobot Create

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Hello,

I am running an iRobot Create with the Brown driver and Sparkfun's 9D Razor IMU. To talk to the IMU I am using Adam Stambler's imu_9drazor package. The Brown Create driver successfully provides odometry data on the /odom topic and I can teleop the robot on the /cmd_vel topic. The imu_9drazor node successfully produces data on the /imu and /imu/imu_raw topics. Now I'd like to combine the two odometry sources using the robot_pose_ekf package. However, when I launch the robot_pose_ekf node, I get a stream of error messages like the following:

[ERROR] [1301063933.943333309]: filter time older than odom message buffer
[ERROR] [1301063933.998367333]: Covariance specified for measurement on topic wheelodom is zero

The launch file I am using to bring up the robot_pose_ekf node is as follows:

<launch>
  <node pkg="avr_bridge" type="bridge_node.py" name="imu_node" args="$(find imu_
9drazor)/config/imu.yaml">
   <remap from="imu" to="imu/imu_raw"/>
   </node>
   <node pkg="imu_9drazor" name="imu_msg_converter" type="msgConverter.py">
     <remap from="imu_raw" to="imu/imu_raw"/>
   </node>

  <node pkg="robot_pose_ekf" type="robot_pose_ekf" name="robot_pose_ekf">
    <remap from="imu_data" to="imu" />
    <param name="freq" value="10.0" />
    <param name="sensor_timeout" value="1.0" />
    <param name="publish_tf" value="true" />
    <param name="odom_used" value="true" />
    <param name="imu_used" value="true" />
    <param name="vo_used" value="false" />
    <param name="debug" value="false" />
    <param name="self_diagnose" value="false" />
  </node>
</launch>

Any thoughts on what I am missing?

Thanks!

patrick