After loading my site www.FlashUser.net ( wordpress 3.5 ) in a browser and click on a category from the top categories ( Css, Freebies, Inspiration etc ) I see this link in the browser:

http://www.flashuser.net/_index ( which does not exist in my site, I guess is the default 404 page )

If I click on the Css category the correct link should be http://www.flashuser.net/category/css ( as you see when mouse over a category in the bottom bar of the browser or page source )

If I click on the Freebies category the correct link should be http://www.flashuser.net/category/freebies

and so on

I have addressed this to the hosting support couple of times but none knows to give me a solution on what is this and how to solve it.

( sometimes the category pages loads correctly but most of the time this _index url is displayed, the rest of the site pages loads fine )

Hope someone has an idea and can help. Thanks.