When I hover over a page I am looking....

When I hover over a page I am looking at, I see the url a little bit different. Instead of seeing:
http://mywebsite.com/mypagename
I see
http://mywebsite.com/%pagename%
And if I click over this page url I get a error (bad request error 400)
quote==================
Bad Request

Your browser sent a request that this server could not understand.
Apache/2.2.16 (Debian) Server at h4bs.com Port 80
unquote==================

I have another website but it works correctly.

How to get it wowrking properly....

Thanks!