i have installed ispconfig in another server, and jailkit works fine.
i think the only differences between the testing server and my production site are this:
-in the production server, where didn't work jailkit, /home is a soft link to /usr/home:
lrwxrwxrwx 1 root root 10 abr 16 2010 home -> /usr/home/
-in production server, quota is not enabled (don't have the /quota.user and /quota.group files).
maybe one of these differences could be the reason to fail jailkit?