I need help with a Trailhead challenge that I can't get a pass on:

• Create an approval process to support a case escalation procedure, with the ability to approve directly from Chatter.Verify Chatter Approvals is enabled and the Case standard object has Chatter feed tracking turned on.
• The approval process must be created on the Case object and be named 'Case Escalation'. No entry criteria is required for this approval process and you can set yourself as the approver.
• Upon entering the approval process, approval request notification needs to be posted to the Chatter feed.

This should be so easy! I can clearly see that the approval process is working and that it appears in the feed, but I still get an error. What am I missing?!

Challenge not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Process failed. First exception on row 0; first error: NO_APPLICABLE_PROCESS, No applicable approval process was found.: []

Appreciate any help!