Can you explain what you were doing when this error happened?
Where/how is the error displayed?
Trying to open/download this file using a browser (which one) seems strange. If you were doing a manual/auto update anything like this should be done in the background, not in a browser to give a 404 (page not found) error. An avast! repair should also work in the background.
So it may well be that that page/file no longer exists in that location.