Tutorial:
1. Remove all cert file from the system folder
2. Unpack iocerts.zip (do not matter where)
3. Open the certmgr.exe and remove all cert in that window (which is of ioFTPD)
and close window
4. Open now the rsa_keygen.bat and filled in (Please enter your server's hostname (example: xxx.dyndns.org)
ioFTPD and press enter
Please enter your sitename: here the same ioFTPD and press enter
5. The file is created in folder iocerts
6. Replace that file into the system folder.
7. Done (restart your server).
Open your ioFTPD.ini (system folder) and look here:
Require_Encrypted_Auth = *
and
Certificate_Name = ioftpd
Good Luck