Are you skipping the task after completing it? or replacing the .complete with the .skip= You should skip a task when it is "Created", "Ready", "Reserved" or "In Progress", not when it is completed.
I have made a simple test for skip:
https://github.com/calcacuervo/JBPM5-Samples/blob/master/human-tasks/src/test/java/com/test/HumanTaskTest.java test skipHumanTask(), and works fine.
As demian mention, you are getting that exception because it's not allowed in the cycle to move that task from the Obsolete state using the Skip action.
Ok, now it works, thank you, however I still have this error when I try to abort a sub-process.
I have recreated the problem, I attach the processes files and the log.
Why the script Task "abortSP" is executed more times?
Thank you, I hope you can help me again!