Snow Leopard - Dock icons randomly disappear

That has happened to me with the Mail and Address Book icons, they became invisible but the blue dot would remain when the apps were in use. It seemed odd that it would happen with the two Apple apps.

My procedure for correcting the problem affects only the app with the problem.

• quit the app
• right click (I have a two-button mouse) on the invisible icon
• chose 'Options - Show in Finder'
• chose 'Options - Remove from Dock'
• rebooted the app from the Finder window
• chose 'Options - Keep in Dock' and moved the icon back to its original place.

That immediately corrected the problem. The icons remained after reboot.

Open /Applications/Utilities/Terminal and enter the following case-sensitive command:

killall Dock

Dock will restart.