Shared Document won't open

[swcss]

I have an Excel document saved in a shared folder on our server. I usually always have this document open and everyone else can open it as read only to view the information they need. This document will not open on one persons computer while I have it open on my computer. The prompt to open as read only never pops up, Excel just thinks... Does anyone know if this is an Excel setting that is different on his computer or any other reason it wouldn't open on his computer?

Thank you!!