there, I have a problem with the author links in the list.

Hi there,
I have a problem with the author links in the list.
1. When I try to click on an author (link) in my listing list, i am directed to the 404 error page, but I want to see the author's profile.
How can I do this?

2. And best off all at the author's profile page I would like to see all listings of this author.

Here is a link: http://wordpress.p195554.webspaceconfig.de/index.php/listings-category/lesergeschichten/

or this:
http://wordpress.p195554.webspaceconfig.de/index.php/listings/

Thanks a lot