Apache 2.2.8
Windows XP PRO SP2 (64-bit)
[Also tested on Windows Server 2003 Standard 32-bit]
mod_auth_sspi 1.0.4
Adding the directive
ErrorDocument 401 /custom-error-page-401.htm
causes authentication with IE6, IE7, or FF2 to fail. Instead of being prompted for a username password the custom error page is displayed immediately.
Removing the directive resolves the issue right away.
I'm not sure if this is due to Apache or with how the module interacts with Apache.