Strange issues where client PC on domain will use intranet sites that use windows authentication for their security. Everything works fine then randomly stops working and won't accept the username/password? (ie. can't get to SharePoint site)
Strangely enough, all mapped drives and everything else network based seems to still operate. Even stranger, if you run a "gpupdate /force" it seems to fix it. Only other solution is log out of windows and log back in.