restrict access to members of the built-in namespace - custom error message?

[Penny]

We are running Cognos 11.0.9 and have our environments configured to restrict access to members of the built-in namespace (this is set to true in config).  If a user that is not in the namespace attempts to access Cognos 11 they get the message "Unable to authenticate.  The provided credentials are restricted from accessing IBM Cognos.  Please contact your administrator."

My question is - can this message or page be customized?   

Any advice or help appreciated.

Thank-you

[sdf]

Ideally there's should be a way. Like editing the XML file where that particular message resides.
You might want to look for that file first. I am thinking something like system.xml.

If the url in which this message shows is a generic url (does not change) for any users. Maybe you can redirect the url into a different URL or a customized page.

I am keen into knowing if this is possible as well.

Hope someone with better experience would see this post.