Common issues:
Have you tried turning it off and back on again?
Do you have the proper CORS headers set?
When setting up Blockstack, it's critical to make sure they have proper CORS headers set on the manifest.json file.
Using uglification?
If you're deploying a web app and using uglification, you need to make sure you must whitelist certain classes. Double check that the tools you're using aren't uglifying your code automatically.