404 error in headers, but blog appears

Hi,

I get a 404 not found error when i access the home page of my blog. But it’s just in the headers, the page appears normal.
I figured out that it has maybe something to do with my blog address which is different from my wordpress address.
I’m not using mod_rewrite, I have renamed index.php to “blog” and that is parsed by PHP. Now “/blog” is my blog address. The problem is there since I’ve upgraded to 2.0.