I have one blog running that works without any problems (wordpress is installed in the root directory of my server). I installed a second wordpress in the folder wordpress_ which is located in my root directory. I've set up my domain to point/route to this folder.
I also checked the config.php for any errors - it's set up exactly like the config.php for the blog that works (except for the details on the new database).
You can check out the blog that's not working at http://www.diefinanzplaner.at.
I read a lot of posts from guys with similar problems but have not found a solution for my problem yet. Both wordpress installs are 1Click Installations. I'm guessing the problem has something to do with the wp install being in the subdirectory but I have no clue where the problem really is.