Can you check if tasks are created in task server (db)?
One of the reason can be that your new users are not registered in task server. Depending on how yo start your task server (if default DemoTaskServer class or web app - human-task-war is used, there are two mvel files that represents users and groups) you need to register users and groups to inform task server about available actors in the system.
So you can either:
- update mvel files (LoadUsers.mvel, LoadGroups.mvel)
- register users via taskServiceSession and its method addUser addGroup
HTH