This can result from namespacing issues in your environment. Your app is called DemoAppp
(note the three "p"s), so ensure that your naming convention adheres to the following:
# app/config/initializers/development.rb
DemoAppp::Application.configure do
Alternatively, if it's possible that DemoAppp
is a misspelling, you may want to replace DemoAppp
with DemoApp
with two "p"s.