OZZY-GS: Take a chisel to one of the flats on your 24mm bolt head and hit it hard in the off (counter clockwise) direction, getting it to dig into the flat. This should "unfreeze" it. You can use a bolt grabber (http://www.sears.com/craftsman-10-pc...1&blockType=G1
) if the head is severely damaged.
CheckarD's advice "Tap it LIGHTLY with a hammer to help it break loose." is a minimum when removing the drain bolt. Some BMW techs say to set your allen key or 24 mm socket in place on a breaker bar and bang it hard on the off direction or lightly in the on direction then hard in the off direction. So OZZY, you are not alone