If your system hangs and the System event log contains:
Event ID: 2019
Description: The server was unable to allocate from the system nonpaged pool because the pool was empty
it may be that an application or service is using a COM port and Serial.sys is allocating memory that it does not release, due to IRQ sharing on COM port devices.
Windows NT does not support this. I do it without any problems (other than a System event at boot) because the shared IRQ COM ports are never in simulaneous use.