After grappling with this problem for many hours I thought I'd better ask for some help...
I installed ISPConfig3 from this
howto, then retraced my steps using the more popular "Perfect Server Debian Squeeze with Bind and Courier ISPConfig3" guide, updating and reinstalling packages where necessary.
I removed the default FTP server (proftpd) which appeared to be installed somehow, but not running, installed pure-ftpd, and then updated ISPConfig to recognise my pure-ftpd installation, which it didn't before, but now does.
At least, it shows up as a listed service under the monitor tab now, however it shows as "Offline".
I watched the console during updating my ISPConfig installation and it did appear to start it with the following command:
/usr/sbin/pure-ftpd-mysql-virtualchroot -l mysql:/etc/pure-ftpd/db/mysql.conf -l pam -D -b -u 1000 -Y 1 -O clf:/var/log/pure-ftpd/transfer.log -E -A -8 UTF-8 -H -B
However if I run netstat, the process isn't listening on any port.
(I can start it manually by running "pure-ftpd-mysql &", and it shows up in netstat. It just doesn't appear to be invoked by ISPConfig.)
I've read a bunch of existing threads on the subject, but couldn't find my answer.
Where do I start trying to troubleshoot this?