REST Server error (unable to locate class session.php)

I setup the RestServer from https://github.com/chriskacerguis/codeig...restserver

Trying to run the api example on my server. Using CI 3.0

Copied the example.php to the directory  /application/controllers/api

Using postman, issued a GET to servername/api/example

I am getting the error Unable to locate the specified class: Session.php. and HTTP Code 503 Service Unavailable 

This looks like a configuration error to me

I have not made any changes to example.php 

Any ideas?

We had a custom controller (my_controller.php) that was causing this error. Once I disabled it, things are working fine on the api

Is there a way to run the site that exposes REST API side by side with that goes through our custom controller?

thanks
Krish