Since before the Magic Mouse update, I cannot install any new updates anymore. Software Update finds and downloads the updates just fine but when I click on the "Install" button, it greys out for a few seconds and then nothing happens, i.e. the install process is never triggered. The same thing happened for the Magic Mouse update, iTunes 9.0.2 and the latest Parallels update. When I wanted to create a new account to see if the same thing happens there, System Preferences wouldn't let me authenticate. When I clicked the lock symbol, nothing happened. I also repaired disk in Disk Utility and although errors were reported and repaired, it hasn't changed anything. Downloading the updates from Apple's website produces the same results, the "Install" button is unresponsive. I'm pretty much out of ideas here as I can't even log in as a different user. I'm on a mid-2007 MBP running 10.6.1. Anyone have suggestions? Thank you.