in fact, my uncle is having the same problem for the past year or so already (or even more than a year)...his work computer, his home computer, and he said a couple of his colleagues also had this problem...but since I could do it no problem, he also thought it's just problems of their own computers...

now it seems there's probably really problems with KA's online checkin system's compatibility with some systems ? although I can't really tell the specific reason...