Other people have had this problem and concluded that it had something to do with having a namespace. But this is a new developer org I set up specifically for Trailhead, no namespace. I am still getting an error on this, I have verified the exact wording, tested the workflow, and saw the task created . But when I try to verify the Challenge I get the following message:  " Challenge not yet complete... here's what's wrong:
The 'Follow Up on Escalated Case' Workflow assign task action was not found."

Other people have had this problem and concluded that it had something to do with having a namespace. But this is a new developer org I set up specifically for Trailhead, no namespace. I am still getting an error on this, I have verified the exact wording, tested the workflow, and saw the task created . But when I try to verify the Challenge I get the following message:  " Challenge not yet complete... here's what's wrong:
The 'Follow Up on Escalated Case' Workflow assign task action was not found."