Just installed v6.1.20's guest additions freezes Mac OS X El Capitan v10.11.6 guest VM & then host.

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Successfully (install/upgrad)ing VB v6.1.20's guests additions in Mac OS X El Capitan v10.11.6 VM cause a lock up to VM and then VB v6.1.20 in an old 2012 13" MBP.  https://forums.virtualbox.org/viewtopic.php?f=8&t=102608&p=498505 for my forum thread in details including logs. To make guest additions install/upgrade not freeze its VM and VB, disabling audio before starting up this VM prevents it. Thanks to fth0 for the answer.

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Logs and a screen shot.

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The forum thread says this is audio related. I can reproduce the same crash if I make the guest VM play audio like in iTunes. If disabling VM's sound settings, then it will not crash.