Some time back the Warehouse was moved which meant that old versions of SketchUp wouldn’t be able to access it directly. In addition, the Warehouse no longer creates versions of components that can be opened in the old versions. The oldest SketchUp version that is supported by the Warehouse is 2014. I’ll hunt up the links for that but the upshot is, if you want to use components from the Warehouse, you’ll need to use a newer version of SketchUp.
See:
https://forums.sketchup.com/t/heads-up-sketchup-8-and-sketchup-2013-users/10264/2
You could download the Collada file from the Warehouse and open that in SketchUp 8, though.