Webredirect.nsf is not working when using IP

Hi,

When login to http://[server_ip]

It will open http://[server_ip]/webredirect.nsf ,

then prompted for username and password.

After entered username and password, it will open email page properly.

But when login to http://[server_name]

It will open http://[server_name]/webredirect.nsf

after entered username and password,

it always prompted back to the same page, username and password again and again and again.

Please advise.

Thank you,

Ivan.