Just come across a weird issue here, where am getting a problem with one domain's ftp users unable to ftp in to the server.

The logged error is
proftpd[21129]: virtual.overflow.net.au (127.0.0.1[127.0.0.1]) - no such user 'yoda@australianmotorsportsforums.com.au'

This user does exist in my ispcp database, and at one stage did work fine, but suddenly it has stopped working.

I've stopped and restarted proftpd, and that's made no difference.

Anyone come across this issue before ?

Well, I'd try to log, what the mysql server sees... (mysql log enable - only for the test! log will be quite big with the time...)

then you can decide how to go on...