Canon 550d focusing problems??

[swanseamale47]

Went shooting with my friend yesterday who uses a 550d, it's got an odd focusing problem. It hunts for a while, snaps into focus but it's miles out (front or back focusing) and I mean miles out (subject totally blured).
Oddly in full auto or the scene modes it works fine, focuses bang on every time (and fine in live view), her lens worked perfectly on my camera and my lens had the same issues on her camera, so it's a camera problem of some sort.
I've gone through the menus and cant see anything obviously out. It appears to be something thats different in auto and live view from the normal AV Program etc.
Anybody got any ideas, I'm baffled, my best guess is she's altered something somewhere in a menu but I'm dammed if I can figure out what.

 

[Box Brownie]

Not sure but to eliminate an odd setting......factory/default reset? Having said that I have never had the need to do it on my Canon bodies so 'where in the menu' ?

 

[Canon Bob]

One possibility is that there's dust on one of the AF sensor pairs. In auto mode it'll try all the sensors and pick the one/ones covered by the nearest subject and thereby ignoring the one that's possibly inoperative. Liveview will bypass the system completely.

Bob

 

[swanseamale47]

Thanks guys.