Heroku Logs Insight

Heroku Logs Insight

My Ruby on Rails app was running smoothly until yesterday.
When ever I try to open my Heroku App it gives me a "Application Error"
message and when I check my logs I get this message below.
[36m2013-09-10T17:42:34.393159+00:00 app[web.1]:©[0m Connecting to database
specified by DATABASE_URL
[36m2013-09-10T17:42:34.846457+00:00 app[web.1]:©[0m Exiting
[36m2013-09-10T17:42:34.849786+00:00 app[web.1]:©[0m
/app/vendor/bundle/ruby/2.
0.0/gems/devise-3.1.0/lib/devise/rails/routes.rb:440:in
`raise_no_secret_key':
Devise.secret_key was not set. Please add the following to your Devise
initializer: (RuntimeError)
Has anyone encountered this? What does the error mean?