An error occurred in the application and your page could not be served.?

I found two web pages that should help you in debugging your code here:

• Causes of Heroku H10 App Crashed Error and How to Solve Them
• Heroku Error Code H10

The first is more detailed and the second links to an anchor on a list of error codes. If you're using Heroku, it's worth bookmarking that entire page. I'm interested to know what your specific issue turns out to be.