Use the [esc] key to make Photoshop behave (CS2/CS3/CS4/CS5)

If you try to use a keyboard shortcut and Photoshop ignores it or delivers an alert message when you know the command should work, you probably have a panel option or a field active. Instead of trying to track down the interference, simply press the [esc] key and try your shortcut again. With any luck, your command will execute as expected.