That sounds weird, can you create a small test that we can use to reproduce that issue?
Can you import the org.jbpm.task.service.DefaultUserGroupCallbackImpl into one of your java classes to see that the class is in the correct package?
Are you using jBPM5.2 or 5.3 or master?
I use jBPM5.3.
I did some new tests and in fact I found that the problem comes from the client side.
When the client creates the task, it as to set up the people assignements of the task, including both recipients and businessAdministrators.
If I add the Administrator user in the server, and if I use the following code on the client side, it works well:
// Set task recipients. List<OrganizationalEntity> recipients = new ArrayList<OrganizationalEntity>(); recipients.add(new Group("The team")); peopleAssignements.setRecipients(recipients); List<OrganizationalEntity> businessAdministrators = new ArrayList<OrganizationalEntity>(); businessAdministrators.add(new User("Administrator")); peopleAssignements.setBusinessAdministrators(businessAdministrators); task.setPeopleAssignments(peopleAssignements);