I just got the same error. However, then something popped up about Notification access, and when I granted that to Tasker, DND All worked. If you search for Notification Access in Settings, and set it for Tasker, I think DND All will then work.
I was having a similar problem. However then something popped up about granting Tasker Notification access, and when I granted that to Tasker, DND worked again (I could see erorrs when I ran the task manually). If you search for Notification Acess in Settings, and set it for Tasker, I think DND will then work again.
-Rich B