Yikes. I'm having the same after a dist-upgrade to Etch. The ProFTPd/MySQL connection is completely hosed.
Removing and reinstalling the proftpd and proftpd-mysql packages (DB tables still in place), disabling IPv6 and adding the SQL lines to proftpd.conf, then restarting proftpd doesn't seem to work.
ProFTPd shows in /var/log/proftpd/proftpd.log as started. No errors. There were no errors at the command prompt when it started. When I try to log in I get:
421 Service not available, remote server has closed connection.
Something is _very_ broken with Etch and this how-to