Activation Query with USB devices

I have Vista Enterprise x64 installed and have been running both VMWare 6.0
Beta workstation and MS Virtual PC 2007 as I needed access to 32-bit OS's as
well as 32-bit with USB 2.0 support for compatibility issues. Probably about
6 times I added and removed my USB 2.0 device in VMWare, which was detected
to be add/removed in both the guest and host OS.

When looking through Eventviewer, I noticed that the following logs are
being added:

Source: Security-Licensing-SLC
Logged: 30/03/2007 04:43:56
Event ID: 1025

Grace period has been started. Grace days=30 Grace type=4.

Whilst my MAK Enterprise key has 15 activations, 12 of which remaining, it
is worrying me that using a virtual OS is flagging possible activation errors.

I say errors because my install is still activated, and running slmgr -dlv
from the command prompt shows my install to still be fully licensed.

Can someone shed any light as to why the above log is appearing? Thanks.