I've fortunately not had a problem with my corny kegs. It sounds like you've got an issue with the kegs or your sanitizer, or both.
Do you and your friend sanitize the same way? I highly recommend StarSan for sanitizing and Oxyclean for cleaning. Oxyclean is a basic cleaner and after a thorough rinse coupled with the acidic StarSan, there's nothing left to interfere with your beer. I also pour about 1 gallon of sanitizer into the kegs, pressurize, and let that sit until I need it.