I am doing the angular2 tutorial at this address: https://angular.io/docs/ts/latest/tutorial/toh-pt3.html I have put the hero interface in a single
angular2
hero
The error is because you have not saved the files after creating them.
Try saving all the file by clicking "Save All" on the Editor.
You can see the number of files which are not saved by looking below the "File" menu shown using blue color.