Concensus from the Prof. Flight Training show at Heathrow was that you'd have to resit -ALL- your exams again.
Bit of a pain if you've aced 13 of them and failed the 14th four times!
If someone is still not getting it after three attempts (unless there's something really screwy with the exam paper) I'd be questioning the groundschool - after all, before you do the exam they should be able to tell if you have a good chance of actually passing it.
HTH
Ivan.