My mac volume level won't change after sleep

My "Line Out" (2.1 Speaker System) does not seem to accept volume changing commands either by the Apple Wireless Keyboard, or System Preferences > Sound. This happens all the time after I put the computer to sleep. Before when I switched to Internal Speakers then back it would "unlock" and let me adjust the volume, but that is no longer the case (I should point out that the volume controls are not disabled, it's just that changing the level does not do anything). I can however adjust and use Internal Speakers just fine. This forces me to restart my computer in order to adjust the volume again.