File access

Hi,
Today a user came up to me and said that she couldn’t save a file that’s on the network. The file is a drawing made in AutoCAD and saved on a netgear drive. It turns out that someone else was using it therfore not alowing her to save her changes. There was no reason why anyone but her should have been using it at that time.
My question is there a way to find out who’s accessing a file using a command line or a script? Any tips would be helpful.
Thank You