No access to some folders "403 Forbidden"

[beton-schwimmt]

Hi,

i have some problems with my wordpress blog. I can open the main page http://beton-schwimmt.freeunix.net/wordpress/ but if I try to log in, on http://beton-schwimmt.freeunix.net/wordpress/wp-admin , I get a failure message: 403 Forbidden ; You don't have permission to access /wordpress/wp-login.php on this server.
This address appears:
http://beton-schwimmt.freeunix.net/word ... F&reauth=1

How can I fix this problem. If it's impossible to me to fix it, can you (admin) fix this problem? Without the abbility to log in, the blog is useless...
I've read something in this forum (viewtopic.php?f=6&t=4). Is my problem similar to this one?