ISAPI Filter Won't Protect One Site

[Klingenstein, Nate]

All,

I'm bad at IIS.  Please forgive.

We have a basic SP configuration that protects 2 Sites.  Requests to protected locations on the first Site work fine.  Requests to the other site are never protected.

I've checked the Site mappings many times.  I've made sure the filter is present and enabled for that Site.  Everything worked in dev and stage with apparently identical configuration(beyond hostnames and site ID's).  Everything works if I access the content on the main Site.

Other people get to touch this IIS configuration.  I'm fairly sure the Shibboleth configuration is right.

I have no answer beyond that "something else" in IIS is preventing the filter from working on that Site.

Does anyone have any ideas?  Thanks in advance,
Nate.