rolyatnitram on "new pages give 404 on PC only but not ona Mac"

I have a site which has been up and running for a few years. I recently updated to WordPress 3.6 and don't recall making any other changes. Now when I create a new blank page I can access it fine from any browser on my Mac, but when I try any browser on a PC I get a 404 page not found error. Weird !

Here is a sample blank page:

http://www.orcaspets.org/random-page/

Any ideas???

Thanks Martin