I think they say on the packs that it could be a false positive because it could be an evaportaion line. Normally though if there is definatly a line there it is positive and HPT can't get this wrong because there is only 1 thing that could cause the hormones to make the test turn positive.
If the others have been negative, I'd leave it a few more days and test again. It could just be that your HCG just isn't strong enough yet& needs to build up some more and you tested the first time with some stronger urine than the other times so it was more concerntrated.
Sometimes you can get a faint positive and it goes because unfortunatly baby didn't stick & thats really common around the time of AF. Lots of women concieve and don't know about it because it never gets as far as taking a test.
I know it's easy to say and harder to do but try not to let it play on your mind too much. See if you can find plenty to do to distract yourself till you test again.
Good luck.
