I have the exact same problem on one of my 4 network machines.
I use machine A.
I realized the problem when I built a new machine B, and tried to copy some files from machine A.
Machine A hangs whenever I start to copy any file from it. Copying from B to A again hangs only machine A. (System hangs including the mouse cursor-ctrl+alt+del doesn't work-it's just hard hang)
I just connected a machine C and tried to do the same. I could copy a few files this time. But it's again the same. (I'm trying to copy files from shared drives. All drives are visible you can explore the disks but whenever you start copying, ONLY machine A hangs.)
:( I'm stuck.
In order to copy files I use either msn or teamviewer remote desktop application for data transfers on my LAN. This is funny and sad.