That is odd. There are some diagnostics we can do. Can you open the view: Type Space view. You should see a ExtJSTL-4.1.1.zip in this view.
Make sure you are in the VJET perspective.
Go to Window -> Show View -> Type Space
If this is not showing up then maybe the file is corrupt / having issues being read in. Try deleting the project (and the files on disk) and downloading the zip again.
The dependency won't work as an archive.