Filip,
Did you do a fresh install, then a restore, or just a fresh install. Webmail works everytime a do a new instal on my test box with 6.0. The problem may be with your horde password. I can duplicate this error message if I change my horde password. Before 6.0 the default horde password used to be horde. So if you did a new install, then a restore, chances are you need to go to /home/httpd/html/horde/config and change the password to horde. If that works, then you should be able to do
/sbin/e-smith/db configuration setprop horde DbPassword horde, then
/sbin/e-smith/expand-template /home/httpd/html/horde/config/horde.php.
If the above doesn't work, then this is probably the thread you need to follow:
http://forums.contribs.org/index.php?topic=20210.msg79505#msg79505Good Luck,
JB