Mark II AF question

I recently joined the Canon world with a Mark II. I finally had some
time to take it out and play sunday, but the results were frustrating.
I was shooting my wife and son on our swing set. I set my focus point
to the far right point, and shot vertical. I was dead on my son's face.
I shot a bunch of pictures this way, and none of them are in focus. All
backfocused. I was shooitng with a Sigma 70-200. Later that night,
i reset all custom functions, and shot a few more off the center square,
of my cat. Pictures are dead on sharp. so, this morning, I brought the camera in with me, and used one of our Canon 70-200s and tried the same test, sure enough, OOF pics. Front focus. My camera performed fine with
a 24-70L on it, on all focus points. Is this a problem related to longer focal
lengths of zoom lenses, or do I need to send my camera in to be checked. I bought it as a refurb from B&H two weeks ago. Sorry for the long winded post. I am still learning the system, and trying to rule out user error. Here are the pics:

http://homepage.mac.co​m …/.Pictures/sigm​afocus.jpg
http://homepage.mac.co​m …es/.Pictures/MA​0W6547.JPG

I tried to look at the photos but the link was dead. I'd suggest attaching them to your post rather than linking to a flaky external website. Note that the maximum size of images you can attach is 800x800. If you want people to look at detail such as whether or not something's in focus then it's probably best to crop out a section at 100% rather than reduce the whole frame to 800 pixels.

Based on one lens all doing back focus and one lens doing all front focus and one lens being right on, I would guess the lenses need calibration, not the camera.

But before blaming anything do the ruler or newspaper test to check just to make sure.
How to do it is described somewhere around here. But simply take a ruler set it at about 45 degrees to camera focal plane add a focus object (such as a pen or a newspaper) about the half way point on the ruler and from a tripod or other stable seting take at least 3 images of the object from 3 meters (10 feet) away, wide open, and see where the focus falls on the ruler relative to the object.