I keep getting this error from the challenge.  I logged into my developer console from the Trailhead challenge screen using same email address (only have one on Salesforce.com) and nothing has changed since I started the developer track on Trailhead, which requires numerous challenges.

The Apex class named StringArrayTest shows up on the development console and from the setup interface in the developer section....

I am puzzled how it can show up on both and after entering from the trailhead challenge logon to developer edition and still have this error that is is not  found.  Any suggestion????