Well,
I have made some minor changes to the standard osX setup,
running php, ipfw firewall (to defeat some unspecified piece of software's piracy-detection schemes), portsentry (cos I'm paranoid), nothing special.
I also liked testusers 'ftponly' script. But now the ftpusers I made this way cannot login anymore....hmmmm.
Reason 1 was found quickly: the file /etc/shells was replaced.
As I have my ftpusers default shell set to /dev/null is just had to enter that.
Okay, so far so good: the " ftpuser may not use ftp " error is gone, to be replaced by: 'can't change root'
Why...
My guess:
-the ftpd process does not have the right permissions to run chroot
Am I right? How would I change that?