Probably one of the worst and most frustrating bugs.
Turns out computeSpectrum will NOT work if ANOTHER Flash is using audio. Meaning if you have a Flash that using SoundMixer.computeSpectrum one of those super annoying security sandbox runtime errors will pop up on the browser if YouTube, GMail, or any other Flash using audio is opened.
The fix? There is no fix. No, security.allowDomain won’t work. No, placing crossdomain.xml all over your server won’t work either. The only thing one can do is catch the error (or use areSoundsInaccessible()) and have something else happen in between. This bug is especially annoying for game developers like me who are working on a game that uses the computeSpectrum to generate content…
Grrr… So annoying.
Encourage Adobe to fix this by voting for it.