Canon Extenter Capatability
I recently purchased a Canon Extender EF 2X Mk III from ProCameraShop for use with my EF 70-200 F4L IS USM lens
I have noticed the IS and AF functions don't work when using the extender. Is this becasue this is due to incompatablity or have got a "Grey" Dud product from the ProCameraShop?
No, this is perfectly normal. It is because your camera isn't capable of AF with a lens that has an f/8 maximum aperture (which is what the f/4 + 2x extender combination gives you). Only the 1-series and the 5Dmk3 are capable of AF at f/8, and even then only with the centre points.
There is a workaround. You can tape up the contacts on the extender so that it doesn't report the aperture to the camera. The camera will then attempt to AF, but don't expect miracles since it is likely to be unreliable and slow.
[ edit: I see you mentioned IS too. As far as I'm aware that should still work for that combination. There's a compatibility chart here: http://www.wexphotographic.com/blog/canon-teleconverter-compatibility-chart ]