When troubleshooting unexplainable behavior in Windows NT, you may have to disable your ant-virus software.
When disabling the anti-virus software, it is not sufficient to just stop the service, you must also stop the device drivers in Control Panel / Devices.
While different versions of the software may have more or less device names, here is a partial list:
|Norton||NAVAPP, NAVENG, and NAVEX15 (for Microsoft Exchange Server)|
|Inoculan||INO_FLPY and INO_Fltr|
|McAfee||NaiFiltr and NaiFsRec|