When trying to access a document that has been attached by a teacher via FAWeb, the parent is brought to a login screen for FAWeb. Has anyone else experienced this problem?

I have had a number of parents say that when they try to open a Shared Document in a Class on NetClassroom, they get a "page not found" message. Not all parents have this problem. I login as the parent and it works fine. I have had them check such things as making sure they have Word installed...