A task in the process or process template is a leaf task, but has subtasks. This is forbidden.
Possible Causes and Suggested Actions
All TeamworkIQ tasks are either "leaf" tasks, which must never have subtasks, or "list" tasks, which must always have subtasks.
Leaf tasks include:
Leaf tasks MUST NEVER have any subtasks.
List tasks include:
List tasks MUST ALWAYS have subtasks.