ReferenceError: Router is not defined

Exception while processing message ReferenceError: Router is not defined
    at http://localhost:3000/client/todos.js?c91fcc0a8bde02202637577df27254117e298b56:29:7
    at http://localhost:3000/packages/livedata/livedata_connection.js?ea1a42f17f205bb759d07ec7f699138e4f98c3a1:491:47
    at Array.forEach (native)
    at Function.<anonymous> (http://localhost:3000/packages/underscore/underscore.js?772b2587aa2fa345fb760eff9ebe5acd97937243:76:11)
    at http://localhost:3000/packages/livedata/livedata_connection.js?ea1a42f17f205bb759d07ec7f699138e4f98c3a1:491:22
    at Array.forEach (native)
    at Function.<anonymous> (http://localhost:3000/packages/underscore/underscore.js?772b2587aa2fa345fb760eff9ebe5acd97937243:76:11)
    at http://localhost:3000/packages/livedata/livedata_connection.js?ea1a42f17f205bb759d07ec7f699138e4f98c3a1:489:11
    at Array.forEach (native)
    at Function.<anonymous> (http://localhost:3000/packages/underscore/underscore.js?772b2587aa2fa345fb760eff9ebe5acd97937243:76:11)