UserTaskNotFoundException ... User task is not executable ..., this might be because someone else already executed it.

actually, the flow won't complete:

either by clicking "Abort" or "Accept" (or rather having clicked before: error RS says "current state" is "failed") it stays as "Pending for review":

why that?

[amottier]

Can you share the log file of Bonita Engine available from Bonita Studio Help menu?