[horde] Cant login !

[Andy]

Hello folks,

Debian Etch, Apache 2.2.3, php 5.2.0

Installed Horde Webmail from Tarball.

Situation:

Directly Access from main Horde folder result in:

Firefox -> The page isn't redirecting properly

test.php seems to be ok, session counter works.

Access from main folder /imp result with the Login Screen.

But i cant login. If i enter any (of course existing users too) 
user/password the process is working during many seconds, then the 
process abort and the login screen is up again.
No login failed message !!!!

The setup.php script was working correctly. No error message !

Could you help me, please ?

Thanks a lot,

Andy