The trial period for this product has expired.
It was not caused by the other 101 things detailed on the web that can also cause the issue (e.g. Antivirus, Permissions problems with DCOM - such as detailed here http://msmvps.com/blogs/shane/archive/2008/02/05/the-trial-period-for-this-product-has-expired.aspx).
I'm so used to spurious and misleading errors in SharePoint that the most obvious answer was the last I considered - it may be that the original installer didn't enter an Enterprise Product key during the install process (unbeknownst to you). Before you go trying all the other options, you should check your current license status by going to:
Central Administration -> Operations -> Convert License Type
This will tell you your current license status and allow you to enter your relevant license key (Enterprise or Standard).
In addition to what is mentioned here(http://technet.microsoft.com/en-us/library/cc263204.aspx), you also have to do an iisreset to get the error to disappear.
DDK
