Front derailleur range suddenly has become very short For a while when I was riding, there was a stiff feeling changing from medium to high on the crank. Yesterday it wouldn't change at all.

I checked the adjustment of the High and Low screws by following a few tutorials on line (basically, I put it into low and moved the derailleur so that the inside of it was about .5mm away from the chain and adjusting the barrel screw). This was fine, but the problem still exists: the derailleur would not move into high range.

I released the cable altogether to check the gear selecting mechanism on the handlebar its self. All's fine there too - it moved freely.

Next, I moved the derailleur by hand and discovered I still could not get the chain to move to the high sprocket. It's like the derailleur does not have the movement range to move the chain up, even if the chain is rubbing against the inner side of the derailleur.

I checked everything around the derailleur including the two adjustment screws and nothing seems to be getting in its way.

Would anyone know what I could do to fix this?
I had this happen a couple of times. Turned out to be a little rock got in the derailleur mechanism.