I was working on this module 

https://trailhead.salesforce.com/trails/security/modules/salesforce1_security/units/salesforce1_security_monitor 

Under "Hands-on Challenge" I clicked the drop-down and selected "erakeelwani@gmail.com'' ( which is the developer org).  I have created other 2 trailhead playgrounds and when I click on launch they work fine and launch successfully but I am unable to launch developer org when I click on Launch.

I clicked the "Launch" button.

I got a 404 error.

I refreshed the page with the "Launch" button, selected "erakeelwani@gmail.com" and clicked the "Launch" button.

This time I got:

404

TRAIL NOT FOUND

Sorry, that page doesn't exist. Try retracing your steps or review the URL. 

Any help in this regards is highly appreciated