Ember 2.0 upgrade errors: Unexpected strict mode reserved word & handlebars precompile error

I'm trying to upgrade an ember-rails app from ember v1.13 to v2.0. The app loads and templates render in ember 1.13 and there are no deprecations coming through to the console. When I bump the version to 2.0.0 (through the ember-source gem), the app doesn't seem to load and no templates are rendered. Instead, this error is in the JS console: Uncaught Error: ExecJS::RuntimeError: SyntaxError: Unexpected strict mode reserved word If I refresh the page, suddenly I'm hit with a handlebars precompile error:

Uncaught Error: Barber::PrecompilerError: Pre compilation failed for: (prints out file contents) Compiler said: ReferenceError: Handlebars is not defined

Any thoughts on what could be the cause of this? Any input would be greatly appreciated, as I've been stuck on this for hours!!!