FBI Applicant,

A letter reading "not within acceptable parameters" is the FBI's pleasant method of indicating that you indicated deception during your polygraph - meaning you failed according to their terms.

Cave run is correct in that an inconclusive polygraph typically results in a retest initiated by the examiner on the examinee's behalf simply because inconclusive results do not necessarily indicate deception.

Realize that based on what you said was written in your letter and the fact that your examiner said you were having "problems," you likely did not pass the polygraph as opposed to producing inconclusive results.  This is why you have not been contacted yet for a retest.  Rarely will you hear an FBI polygraph examiner use the term "failed" as that would be calling you a liar.  Rather, the FBI wants to make the disqualification more "legitimate" by indicating that you were not within "acceptable parameters."  In a sense, they are trying to align the polygraph examination with the other steps in the process - Phase I, Phase II, PRT/PFT - all of these need a particular quantified "score" to pass.  The FBI would like you to view the polygraph in this same light to avoid calling you a liar.

The appeal process for a failed polygraph is rather informal and can take a very long time.  Before you are scheduled for a retest you will most likely be interviewed/interrogated by an agent to determine your "sincerity."  It is up to the agent to probe you well enough to provide a report that is then used to decide if you will be granted a retest.

Good luck.