Some excel files shared on server open in read only format, and says file in use by (username), when in fact the file is not in use. Only way to save the file is to a new name, then the new file will give the same message when you re-open it. This happens on some but not all excel files on some but not all folders on the network. Have checked permissions and all, they are correct. It just started doing it about a week ago, was fine before that