Windows 2003 Activation - False activation expirey

I`ve just had a win2003 server fail. The error message was:
you have not activated windows within the grace period. etc etc etc.

The server refused to allow any connections, the website it was hosting
failed, so I`m not too happy.

The server was activated many months ago. I rebooted the server, to try a
safe mode boot, but luckily I missed the prompt and the box booted properly,
and I ws able to log in and run without any problems.There`s no hint of an
activation problem, and oobe/msoobe /a confirms that the box is activated.
Anyone have any clues as to what might be going on, and how to stop it...

The server is a Dell 1850, and was built by installing windows 2003, and
restoring a full NTBackup of another Dell 1850 server (including system
state). Both servers had been ativated.

Any ideas to prevent this happening again ?

David Cook