When I went through training, I flunked the GAPAN tests, being told politely but firmly that I had "a very low chance of success during pilot training". I passed over RAF Cranwell the other day with a nice view from the left hand seat at 37,000ft. We were told to believe the results as the tests only give incorrect results to a tiny percentage of people.
Clearly there are no tests out there that are 100% fool proof.
The Oxford tests always receive a huge degree of scepticism on this forum but most seem to miss the obvious point. Most airlines these days will put you through an assessment involving computer/joystick, team exercise, interview, pschye test and sim profile. If Oxford flag up something during their aptitude test, chances are an airline will too (On the day I went through, the guy in charge of proceedings was involved with recruitment at an airline).
They say that whilst personality cannot be changed, behaviour can be modified. I'm not the most natural born leader and I accept that seeing as this is part of my fundamental character, I never will be. However, I have learnt how I am expected to behave and have managed to modify my behaviour sufficiently to progress in this career.
My advise would be to look into what went wrong and work out what they want to see. I found getting the balance right between leadership and team skills was an absolute tightrope.