How to show always 15-20 messages from history chat

[carminexx]

Hi,
I'm using phpfreechat on a website; but when I login with a user, I got the chat blank, and the previous messages are not loaded.
I need that, once logged, any user gets the latest 15-20 messages posted; otherwise he will see only messages sent after its login.
How can I fix this?

Thanks in advance,