vsftpd problem

I am having a problem getting vsftpd working. I followed some basic instruction like http://www.cyberciti.biz/faq/ubuntu-vsf … ce-server/">http://www.cyberciti.biz/faq/ubuntu-vsftpd-ftp-service-server/ and it is currently running in standalone mode. When I connect to it (locally or remotely) through command-line ftp, I get the following:

Connected to localhost.

500 OOPS: child died

ftp>

This occurs before even being prompted for a userid.

Any ideas what to check? I've searched Google extensively but very little seem to apply to this error before login.