Cannot view htm file

A manual in one of our department was place to one of our server last week and everyone can view it. This manual was created on htm file.

This morning, 3 users reported they can not view the file at all. “Error can not find server” the server called “db server” is there! These 3 users can access other program from db server. Checked the links & shortcut from all desktop everybody have the same.

Anyone encounter similar problem? Why they get this error!