I could use http://mydomain.com/chat.aspx to access, all the files are in the CHAT folder under web root dir

I have this in web.config:
<add key="CuteChat.DataDirectory" value="~/Chat" />



I have a sub domain http://chat.mydomain.com/ , map to the CHAT folder under web root dir
I copied the chat.aspx in this folder renamed it as default.aspx, then I could use http://chat.mydomain.com/ to access, it's ok, but when I click on a room, the link point to http://chat.mydomain.com/chat/CH_MainForm.aspx

How should I change CuteChat.DataDirectory in web.config to make it work? thanks.