I am developing a Rails 4 app using the Active Admin gem for the administration back end. Active Admin in turn uses Devise for user authentication. Now, when I try to deploy the app using `capistrano` on the VPS server, I get the below error:

```
rake aborted!
Devise.secret_key was not set. Please add the following to your Devise initializer:
config.secret_key = '-- secret key --'

```

A Google search does not do much for this error. Any suggestions why it is throwing an error? Should I add the secret key to `devise` initializer, as I cannot find any place to set such config key in `initializers/devise.rb`?