The issue is on the index page not the login page. It could be that session variables aren't being saved properly (a server issue) or the restrict access server behavior may be applied incorrectly on the index page. I couldn't get in with the FTP information supplied, so I couldn't confirm which is the source.
If you attach the index page I could see if I can spot a problem there. Also please check the FTP information for typos since that would be the most efficient route to allow me to test directly.