Oh dear, now I do not believe that was meant to happen. It appears that users of Office 2003 who also protect their documents with the Microsoft Rights Management Service (RMS) have found them so well protected that nobody can open them - not even the person who created the documents in the first place.
Microsoft came clean about the problem in a blog post which reveals that "Starting on December 11, 2009, customers using Office 2003 will not be able to open Office 2003 documents protected with the Rights Management Service (RMS) or save Office 2003 documents protected with RMS".
It appears that users were faced with the following error message when attempting to open RMS protected documents using Office 2003:
"Unexpected error occurred. Please try again later or contact your system administrator"
It has taken a few days but I am informed that a hotfix is now available from Microsoft to unlock those frozen documents. Better late than never, I guess. And the cause of the problem, well you'll love this - an information rights management certificate had expired.