Bed PID autotune not working

I have been trying to get PID working on my hot bed but every time i run the m303 e-1, i get an error "PID Autotune failed! Bad extruder number"

#define PIDTEMPBED has been enabled I don't know what else I have to do to get it working.

Edit: I have rolled back my firmware to latest stable release and I can get it work. However it doesn't work on RC6