[till]

Please do what I suggested to you in #5 if you want to debug the problem.

I guess the problem is that var/www is a symlink to /usr/var/www (and not only /home as you mentioned above) which is a security breach for jailkit so jailkit disables the user.

I recommend that you reinstall the server if you want to use jailkit so that /var/www and /home/www are no symlinks, they have to be real directorys or partitions. As alternative you can try to mount /var/www instead of using a symlink.