It is difficult to help without seeing any kind of errors so a good practice is to always provide server log for analysis. Based on your description it looks like task server experienced some issues after completing first task and is not capable of working on the others. Check server log, you could try to clean up data base (if possible) and re-run the test once again.
P.S.
nice to hear that you looking into BPM and jBPM, I am sure it will get better as soon as you get through initial setup steps...
HTH