Why do I receive Event ID 256 in the System log?

A. The full event ID is

Event Source: PlugPlayManager
Event ID: 256
Description: Timed out sending notification of device interface change to window of <program or service name and/or GUID.>

This event ID is a warning message that you can safely ignore. The warning basically means that an application registered to receive Plug and Play (PnP) device interface notifications but didn't respond to a notification within 30 seconds.