As i said i would do a search about it 20ds seem to have this problem.
Canon 40d shutter button repair.
Necessary tools for this replacement include a philips j000 screwdriver a plastic opening tool and a pair of precision tweezers.
For this replacement the front back and top covering of the camera must be removed to get to the shutter button.
My 40d shutter failed after 16 700 actuations.
Originally posted ages ago.
Yer ive heard of the issue with the 40d shutter button before and it turned out to be dirt under or within the button compartment.
Fix it by your self.