Symptom
After the Software Update control panel presents a list of updates and you click Install, nothing appears to happen and the updates are not installed.
Solution
Do not use the "Update software automatically" feature of the Software Update control panel if the use of a "keep alive" application is required to maintain your Internet connection. Follow these steps instead:
1. Click Update Now in the Software Update control panel.
2. Note the updates that Software Update lists.
3. Connect to the Apple Software Downloads site at http://www.apple.com/downloads/.
4. Download and install each update.
The Software Update feature quits all open applications as part of its preparation to install or update components. Some network connections require an active application to maintain the connection. Virtual Private Network (VPN) clients, and cable modem connections that require a "keep-alive" agent are usually instructed to quit by the Software Update mechanism thereby removing the means for the actual update to be performed. Provisions for several commonly known applications of this kind have been made in order for them to function with Software Update. However, VPN and cable modem authentication mechanisms often differ in their implementation and may require custom client applications. The Software Update mechanism may fail if such a custom application is required to obtain (and maintain) a network connection.