Server 10.5 - FTP Users Can't Log In

I have the FTP service running on an OS X 10.5 Server. I can log in with anonymous, if I turn that on. However, when I log in as a defined user with access to file sharing services, I get the message:

Server said: Login incorrect.
Your password may be incorrect. Please double-check your login settings.

I have checked and reset the password. It is correct. Could there be something about the folders being shared that prevent login?

Thanks.