I fixed this in xubuntu 12.04 by opening up the settings editor, browsing to xfce4-mixer, and first changing active-card string value to "PlaybackBuiltinAudioAnalogStereoPulseAudioMixer" and then created a new string with the following name: "/sound-card" with the string value "PlaybackBuiltinAudioAnalogStereoPulseAudioMixer" which worked immediately.
I fixed this in xubuntu 12.04 by opening up the settings editor, browsing to xfce4-mixer, and first changing active-card string value to "PlaybackBuilti nAudioAnalogSte reoPulseAudioMi xer" and then created a new string with the following name: "/sound-card" with the string value "PlaybackBuilti nAudioAnalogSte reoPulseAudioMi xer" which worked immediately.