Strange problem – content not found

I have a strange problem with my blogs. When i point my browser to http://www.mydomain.com/blog i get no content but my layout displayed. When i go to mydomain.com/blog (without the http://www.-prefix) the blog displays fine – both with content and layout.

In the options panel i have specified the blog URI to http://www.mydomain.com/blog. I have also tried with different themes…

I have experienced the problem on linux in firefox and in windows in ie and firefox. It only happens to my wp-blogs, not any other stuff.