Backtrack. Try commenting out everything except the lines
In particular, I am leery of that huge wad of Type and Handler lines. (I added an AddType line when I started using includes, but I later learned it isn't necessary. Doesn't do any harm, though.) I suspect they're colliding with each other, especially with that FilesMatch envelope that seems to say the opposite of what everything outside the envelope is saying.
Are you doing this on your live site? I strongly recommend getting a pseudo-server like MAMP or WAMP. You will sometimes come to grief if the pseudo-server uses a different php than your live server, but for straight html it should make no difference. And it will save you a lot of time being able to test everything on the fly.
:: wandering off in search of a moderator because this question will have better luck in the Apache forum ::
There's an oldish thread in Apache about SSIs. Apparently there's a certain amount of black magic involved-- the kind where it only works on alternate Tuesdays when you stand on one leg and turn around three times and speak to the server in a particular dialect of Quechua. But once it starts working it will continue to work.