@jcollum: If you use appdynamics 4.1.8, the Node version you use has to be under 0.12.9
Try to run `$ node --version` to see your current version.
You can force downloading 4.2.1 if your app run with Node 5.7.1 or less.
`npm install appdynamics@4.2.1`
But by doing that I'm afraid it might not connect to the controller unless you contact the support.