I've had this trouble in the past. I found that if you push the boot lever towards when car is unlocked then lock the car with the fob. Then unlock it with the fob it should hopefully get the catch to work again. You may thave to try it a few times but it does work. To stop it happeneing again I just make sure when I close the boot I push the boot lever towards the car. I think by doing this it re-aligns the boot catch properly. Hope this helps and you get it sorted.
have u tried the key ? instead of the alarm fob ?