I have no clue but I have a question and a proposal. Why are you using jBPM 3.2.2 although jBPM 3.2.8 is the most recent stable version? Maybe you should switch to using jBPM 3.2.8 to try this. Chances could be higher finding other people running or trying to run jBPM 3.2.28 on JBoss 5.1 than that there are chances to find other people using 3.2.2.
Just my 2 cents.