http://www.inicom.net/pages/en.ioftpd-kb.php
Q: What does "530 Login failed: The operation completed successfully." mean on login ?
A: Check your .vfs (admin.vfs or default.vfs)
The first line (your / path) has an invalid real path, or you simply didn't define a / mount point.
Also make sure you didn't delete ioFTPD\text\ftp\login.msg