I have lost 3 days trying to fix the problem upgrading to SP2.1 since it messed up Windows Installer and wrecked my entire OS. I have now reinstalled my OS, all my programs, updated SW 2009, and have moved on to updating SW 2010, but am encountering the same problem. I am at the end of my rope and have no idea what to do. I've attached the install logs, and the error message. Can anyone help me???