Source:  NWCONFIG.NLM

Explanation:  The disk probably is being used by another process.

Action:  Wait to see if the process releases the device, then retry the action. If there is a disk device error, unload NLM programs (except device drivers) that might be using the disk. Then dismount volumes from the disk. If these efforts fail, try loading MONITOR, deleting all user connections, and disabling logins.