NavExcel is a hijacking program. Instead of you receiving "404 errors" you will be redirected to navexcel or navhelper.
To remove this parasite (and it is a parasite not a product) go to Control Panel > Add / Remove Programs. Find NavExcel and click remove. Then when it has removed the files, reboot your PC.
It is straight forward to remove. Just like uninstalling anything else. It's just a shame that the small minds at NavExcel can't think of a better way of promoting their "service".
Craig T
February 2004