First thing I would do would be to separate the forend Iron from the wood. Needless to say remove all the screws holding the Iron to the forend wood then place the forend in a polythene bag then place in a freezer for a couple of days. Remove it and let it warm up to room temperature for two or three hours, then repeat back in the freezer. As the metal shrinks with the cold and the wood changes very little, this usually brakes the metal wood bond. After a couple of freezer treatments, and while the metal is still cold try to part the metal and wood.
With the wood removed you will soon be able to see what the reason is why the forend wont remove by operating the release button.
Simple but very effective method of parting metal components from wood.
