Error assigning a python quaternion

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Hi,

I have tried to setup navigation stack to work with the robot from USARSim the same way as in tutorials, but when I start robot_configuration.launch and move_base.launch I get this error related to odometry:

Traceback (most recent call last):
  File "/home/my_name/ros/usarsim/nodes/my_robot_nav.py", line 127, in <module>
    pub_odom.publish(odom)
  File "/opt/ros/diamondback/stacks/ros_comm/clients/rospy/src/rospy/topics.py", line 677, in publish
    self.impl.publish(data)
...
    buff.write(_struct_7d.pack(_x.pose.pose.position.x, _x.pose.pose.position.y, _x.pose.pose.position.z, _x.pose.pose.orientation.x, _x.pose.pose.orientation.y, _x.pose.pose.orientation.z, _x.pose.pose.orientation.w))
AttributeError: 'numpy.ndarray' object has no attribute 'x'
[usarsim-1] process has died [pid 11052, exit code 1].
log files: /home/hrvoje/.ros/log/1bf16950-642a-11e0-894b-000c29c48bc7/usarsim-1*.log*

Section of code that publish odom:

odom_quat = tf.transformations.quaternion_from_euler(0,0,some_odom_theta_data)

odom.header.stamp = rospy.Time.now()

odom.header.frame_id = "odom"

odom.pose.pose.position.x = some_odom_x_data
odom.pose.pose.position.y = some_odom_y_data
odom.pose.pose.position.z = 0.0
odom.pose.pose.orientation = odom_quat

odom.child_frame_id = "base_link"
odom.twist.twist.linear.x = 0.0
odom.twist.twist.linear.y = 0.0
odom.twist.twist.linear.z = 0.0
pub_odom.publish(odom)

My odometry returns only position and orientation, but not the values for velocity!

Any suggestions will be helpful. Thanks in advance. hv