You may see an error when dragging and dropping tasks/subtasks that the tasks cannot be moved. Here are the following cases where an error can occur:

• If you move a task into another task that is in the Trash
• If you move a task in the Trash into another task
• If you move a task into a subtask that is 3 levels deep (a subtask of a subtask of a task)–the maximum is 3 levels of tasks/subtasks
• If you move a task that has subtasks into another task or subtask such that it would end up with more than 3 levels of tasks/subtasks
• If you move a repeating task into another repeating task–only a task or its subtasks can repeat, not both
• If you move a repeating task into a subtask that has a repeating parent task–this would end up with a repeating subtask inside a repeating task, which isn't supported
• If you move a task into one of its own subtasks–no infinite loops here!
• If you move a task into another of its "series"–for example, a repeating task into another instance of that task (even if it no longer repeats)

Note: Subtasks are available exclusively for users. Learn more about Pro features