Couple of days ago we got following trouble message when connecting to TFS from one of our PCs:
TF30063: You are not authorized to access Microsoft-IIS/6.0.
Gooogl'ing brings idea that it is connected with local Internet proxy settings, however proxy was not set directly.
But! We found that some software specified the proxy configuration script setting some local proxy server. We thought about Selenium IDE installed there but aren't sure since have it installed elsewhere and no such problems yet.
Anyway, turning the script off solved the problem. We will check if it brings other issues.