IMU is not active for robot_pose_ekf

edit

I am working on robot_pose_ekf. In my robot, IMU sensor is available, but, when want to send IMU messages to EKF as an input, it says "IMU sensor is not active" . Please let me know how can I solve this problem?

looking for node robot_pose_ekf...
Input:
 * Odometry sensor
   - is used
   - is NOT active
   - received 0 messages
   - listens to topic /pr2_base_odometry/odom
 * IMU sensor
   - is used
   - is NOT active
   - received 0 messages
   - listens to topic /imu_data
 * Visual Odometry sensor
   - is used
   - is NOT active
   - received 0 messages
   - listens to topic /vo
 * GPS sensor
   - is NOT used
   - is NOT active
   - received 0 messages
   - listens to topic 
Output:
 * Robot pose ekf filter
   - is NOT active
   - sent 0 messages
   - pulishes on topics /robot_pose_ekf/odom_combined and /tf