IIS: Access Problems

We have just implemented an educational software program throughout our School system that use a web interface and requires IIS on our domain controllers at 38 different schools. After implementation and adding the IIS component all but 2 our our schools can access the program via a web browser. When we try with the 2 school that can’t access we get a 3 line domain logon screen. It works fine if you put in the administrator username and password, but we cannot use the anonymous IUSR accountwithout this logon coming up. We can put in the administator account in IIS security access properties and we access fine, but then we have security issues. If any one has a suggestion please let me know.