Attached screenshot is self explanatory.
The problem occurs when custom code calls startJavaProcess and the className isn't set properly in the ProcessInfo parameter.
The error is confusing because the result is that the PackOut process is run instead of whatever Process ID was passed in pi.
I lost some time on checking this, and when I was trying to reproduce I found this https://idempiere.atlassian.net/browse/IDEMPIERE-2958
I thinkg that is clear the answer, so I`m closing this ticket. Feel free to reopen or add some more information if you want