IE8 not asking for authentication to "file://server/share" links

Hello.

I have a web page with HTML code for opening network folders:

function open_win()
{
window.open("file://server/folder")
}

This works properly with XP and IE6 computers, but not with XP and IE8. The user have to authenticate to access the share, but IE8 doesn't ask for authentication, just says that file://server/folder cannot be found. However, if I change the links to just file://server/, then it asks for authentication. If you manually authenticate to the server first, the file://server/folder link works.

I have tried to change several IE options without success.

Thanks in advance.