If you right click on the fader, do you see "Automation Write enable" is checked? There is also visual indication around control elements which are "automation write ready" (since that can be switched individually).
 
Which Automation mode are you using? I mean Inspector/Track/Automation/Write Mode.

You know what, scratch this query... I had been in a hurry and wasn't thinking... I checked it on other tracks and it was fine... this is a midi track. I guess I have to bounce it to audio first.