I thought polygraphs were so well discredited by now that no-one used them; is the FBI still screening with them? What sort of questions are they asking and disqualifying you on?
They are largely discredited, especially for pre-employment screenings. The polygraph exam is the last phase in the Special Agent hiring process, which can take up to a couple of years to complete. Several federal agencies still use it. I can't discuss what is asked, but you can walk out of the exam and know whether or not you told the truth - there is no ambiguity about the answers you give. That is why I am 100% certain it was a false positive.