Only a guess.
I had a similar but reversed problem where I could not release the ratchet when button was pressed so couldn't get the brakes off.
I found the hand grip on the handle had ridden up with use and restricting the button from being pushed down fully to lift the ratchet pawl away from the ratchet teeth.
In you case it MAY be the ratchet pawl is being held away from the ratchet teeth. Othe than that the pawls pressure spring may have broken.
Bob, May 2009
