unknown heroku error

heroku restart

made it work properly again

If problems persists after heroku restart;
Destroy the heroku app and re-create.

As given on http://devcenter.heroku.com/articles/error-codes

H14 - No web processes running

This is most likely the result of scaling your web processes down to zero through the client.

$ heroku scale web=0

Use the heroku ps command to determine the state of your web processes.