On Friday, a bug in the Office 2003 products (Word, Excel, Outlook and Powerpoint) caused users to be unable to open or save files that were protected by the Active Directory Rights Management Service (AD RMS) or by the Rights Management Services (RMS).
An attempt to perform such tasks was greeted by the following message: “Unexpected error occurred. Please try again later or contact your system administrator”. The cause of the bug is the expiration of an Office 2003 certificate.
Microsoft has confirmed the existence of the bug and less then a day later released the fixes, which you can download from here.
The bug didn’t affect Office 2007, so opening the documents with that version was also indicated as an alternative to work around the issue.