Microsoft Dynamics CRM 2011 Update Rollup 6

See link: http://support.microsoft.com/kb/2600640 for the latest rollup 6 for Microsoft CRM 2011.

Note: Update Rollup 6 cannot be uninstalled. Specific database updates are applied during Update Rollup 6 installation that will not let you uninstall Update Rollup 6. You should back up your databases and application servers before you install this update.

Note: Update Rollup 6 establishes a new servicing baseline. This will enable uninstalls of some future CRM 2011 Update Rollups, but this also means that Update Rollup 6 will be a prerequisite for installation of post-Update Rollup 6 Update Rollups.