Microsoft Sharepoint.

Hi i am a consultant and am helping a client that seems to be a sofware error or glitch on sharepoint(maybe settings).

There is 5 outside location shareing 1 excel file. I am in LAX ,3 other computers are in different locations and another computer in Las vegas. They all make editions to one specific file weekly.

Where I am and in vegas have no problems viewing and making editions to a file. But the three other locations can only view but does not have the option to save. why is this? thanks