Since this is a shared file on your network, if anyone has it open all subsequent users who access it will have read only access. This is because it can only be altered by one person at a time. So the person who opens it first has the ability to change it. File opens as read-only. Nope, sorry forgot to say that - no one else has it open.
File opens as read-only.
If not, which I bet it ain't, then your file ACL is hosed. It will either have to be restored from tape backup, or re-created. They can name it something else instead of trying to overwrite the original file. Sometimes this will work. File opens as read-only.