Achieve pass rate of 80% but still fail??

Hi

I am looking for advice, we have used articulate to create an eLearning package which comprises of 3 modules, each with a graded quiz at the end.

We are using AT Learning to pilot the package, and are encountering problems in that the "student" does the quiz, scores 100% or 88% and is told they have failed despite the pass rate being set at 80%. 

They then reattempt the quiz as it is set for 2 attempts and fail again, despite achieving the pass mark.

I have been in and double checked quiz properties and the score is definately set at 80%, can any-one shed light as to what may be happening?

We are running Powerpoint 2003 which I am aware articulate does not like too well, so to speak. 

Grateful for all advice, thanks.