Request.Server variables blank for classic ASP

We are running a classic ASP app, and the upgrade to IIS 8.5 caused our Request.Server variables to be blank:
AUTH_USER
LOGON_USER

Windows Auth is the default authentication type, and server admin has verified all other options are disabled like Anonymous Authentication

Anything else we should be trying?
I saw this in another forum, but not sure how to use:
Response.Write(User.Identity.Name.ToString())

...the above line with User.Identity breaks our ASP page.

Tried both:
<% WindowsIdentity.GetCurrent().Name %>
<% HttpContext.Current.User.Identity.Name %>

...and it breaks the page.