(Shared) File is in use by "username"

I have a user that is complaining that sometimes when they open a shared file, the 'username' field is blank. They are wanting the name of the user to appear every time they open a file, usually excel, that is being used. I am not sure where to start looking - is this problem associated with a setting in the other users' profiles? I am assuming that everyone is logged into their computer with their profiles otherwise they wouldn't have permission to access the share.