Did you use RobotBuilder to generate your code? There is a bug in RobotBuilder-r619, the version in the 2013 WPILib C++ update, that causes newly added subsystems and components to not be initialized in Robot.cpp when regenerating code, as described in
this thread. This bug has since been fixed in r620+; you can download a newer version from
FIRST Forge. You also might want to take a look at
this thread, as it discusses the same or a similar linking error.