Este antigo artigo de suporte da Microsoft diz:
On a computer that runs one of the versions of Windows that is listed at the beginning of this article, if you map a drive to a network share, the mapped drive may be disconnected after a regular interval of inactivity, and Windows Explorer may display a red "X" on the icon of the mapped drive. However, if you try to access or browse the mapped drive, it reconnects quickly.
This behavior occurs because Windows NT Server 4.0, Windows 2000 Server, and Windows Server 2003 can drop idle connections after a specified time-out period (by default, 15 minutes) to prevent wasting server resources on unused sessions.
To resolve this behavior, change the default time-out period on the shared network computer. To do this, use one of the following methods.
Em seguida, ele descreve uma operação regedit que ainda parece válida na minha máquina Vista, mas que não posso testar.