Thingiverse has been having issues lately. The 404 error message mostly occurs with the Zip file that contains all of the files. There is a work-around.

Under the picture, you will see a series of boxes labeled "Thing Details" "Thing Files" "Comments" "Makes" "Remixes" and "Apps". Click on the "Thing Files" box.

You will now see a listing of each individual file. The Zip file is at the top of the list - a button marked as "Download All". That will still get you the 404 error. However, if you click on each individual part's "Download" button, the STL file is available to download.

This workaround seems to work for any of the Thingiverse files that return the 404 error.

Hope that helps.