I just upgraded a SharePoint 2010 site from the RTM load to SP1 (KB2460045) + June 2011 CU (KB2536599). Running the Products Configuration Wizard (psconfig) ended with the following error:
Task upgrade has failed with a PostSetupConfigurationTaskException An exception of type Microsoft.SharePoint.PostSetupConfiguration.PostSetupConfigurationTaskException was thrown. Additional exception information: Failed to upgrade SharePoint Products.
File that under useless error message.
Then I found this post: http://sharepoint.stackexchange.com/questions/16104/sharepoint-server-2010-sp1-psconfig-issue/21031#21031 which suggested to Run As Administrator on the Products Configuration Wizard. That worked.