On an instance of CRM 2011 that was being patched to Update Rollup 6 prior to patching to Update Rollup 8, the following error occurred:
System.Exception: Action Microsoft.Crm.Setup.Common.Update.DBUpdateAction failed. —> System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.
The error was displayed as both a dialog on screen, and within the log file, KB2600640.log located at %APPDATA%\Microsoft\MSCRM\Logs
The solution was to raise the timeout that CRM applied for OLEDB connections from the original 30 seconds by creating two new registry keys at HKLM\SOFTWARE\Microsoft\MSCRM:
OLEDBTimeout (DWORD), value 86400 (decimal)
ExtendedTimeout (DWORD), value 1000000 (decimal)
Then restart the CRM application pool within IIS.
Once the new settings were in place, the upgrade proceeded normally.