I had this problem on mine - the primary latch wasn't moving fully back into the open position after you'd operated the release cable. That meant that the bonnet hook would strike it, instead of engaging into its slot, when you closed the bonnet again.
WD-40 and wiggling it about with a screwdriver solved it - follow the instructions in David C's link.
A good tip is to use a sturdy screwdriver to simulate the bonnet hook - hold it parallel to the ground and push it down into the mechanism to see what is/isn't engaging properly.
Last edited by dmc; 19-05-11 at 01:52.