Shared files not updating on some systems

Hi Guys. Really strange problem. I've just installed 10 new PC's running W7 Pro 64 bit. All 10 have been configured exactly the same yet one of them is being a real pain in the ass. We have a shared folder on a NAS drive. When one of the staff updates a spreadsheet, everyone else who then opens that SS can see the changes, with the exception of this one PC. It can't. It can load the SS...