Weird. Now, I have to manually configure my database.yml in order to make it work on Heroku. Btw, I upgraded from 4.0.0.beta1 to 4.0.0.rc1.

4.0.0.beta1 works fine on Heroku but I keep running into ActiveRecord problem after upgrading to 4.0.0.rc1.

I made this app fresh on rc1, so theoretically that's the difference. Steveklabnik/attendr is the repo if you want to poke at it.