If you have a slow link (or Dial-On-Demand router), you may receive a Semaphore Timeout while using the NET command.
The default time-out value for the Windows NT redirector is 45 seconds.
You can alter the time-out value by using regedt32 to navigate to:
Add Value name ConnectMaxTimeout, a type REG_DWORD, and set it to the number of seconds, in decimal.
You will need to shutdown and restart for this setting to take effect.