I had a same problem. If you click on a network drive via explorer or some other tool (before accessing drive through fox), drive becomes visible.

Problem seems to be in hardware (configuration of network adapters or switch). When I dealed with it sometimes ago and changed adapters everything worked fine.

Better solution is to manualy map drive in a program.

Second solution is (it work where I mapped drive over a internet) is to map drive via IP address such \\192.168.1.1\c not like \\PC\DISK