I have configured a New Relic account for a Rails app hosted on Heroku. Now I want to access the New Relic site directly to setup monitoring for an application not hosted on Heroku. The problem is that it doesn't allow me to sign-up or sign in with my email because it says I already exist with that email.
Do I have to create an independent account with New Relic? Is there a way to manage Heroku and non-Heroku apps with the same account?
Yes, you can use both Heroku and non-Heroku apps with New Relic. Your best bet will be to open a ticket at http://support.newrelic.com and they'll help you out.
Once you're set up, you will land in the non-Heroku account when you log in, but then can switch to the Heroku account. (Links into your Heroku account will work as expected, too.)