Post links do not work without the closing slash ( / )

Very strangely, suddenly, any post in my blog started to give a blank page if it was accessed with the url without the /

So this works fine:
http://personal.al-rasid.com/2012/05/mouad-fencing/

Thies doesn’t

http://personal.al-rasid.com/2012/05/mouad-fencing

I have been using W3 Total Cache when the problem suddenly appeared. I de-activated the plugin, everything back to normal. I am not using any forwarding plugin / settings.

What could it be?