Quit (or if necessary, Force Quit) Software Update.Note: If the issue occurs while installing an update after log out (such as an update that requires a restart), shut down your Mac by holding down the power button, then power it back on.
- Click the Finder icon in the Dock.
- From the Go menu choose "Go to Folder".
- Type: /Library/Updates
- Click Go. The /Library/Updates folder opens.
- Select all contents of this folder and move them to the Trash.
Once the above steps are complete, use Software Update again to re-download and install the update.
To avoid this issue, download and install the Mac OS X 10.5.6 Update or later. Note that this update must first be installed to avoid the issue; the issue may occur while downloading the Mac OS X 10.5.6 Update or later.