My guess is that you are using rvm for your installation. When you do that, you need to do 2 things.
1) Follow the instructions
here to execute rake within the proper rvm environment.
2) Make sure that (if you are using bundler) all of the gems are loaded to your gemset. (EngineY has gems called out in multiple locations).
Once I fixed these 2 problems I was able to execute rake tasks successfully.
Eric