Can you confirm that the device ID of the PDP is '0'? Check the self-test in the roboRIO web-page config.
http://wpilib.screenstepslive.com/s/...ribution-panel
EDIT:
The article mentions that the default ID '0' should be used for PDP.
"Changing the PDP ID while using C++\Java WPILib is not recommended as there is no way to change the desired node ID in the library. PCM node IDs may be set as desired and addressed using the appropriate Open or Constructor of the Solenoid or Double Solenoid class."