Looking at the exception log, it seems that two things happen:
1) The OpenAL object can't be created, for whatever reason. This means that your sound object will be nil.
(This alone would simply mean that the sound won't be played. Which is not good, but still better than a crash.)
2) That 'nil' object is being added to a "NSSet" (might be an internal object), which is not allowed. This is what actually causes the crash.
I guess you cache your sound objects in some collection — is that right? In that case, make a check if "sound != nil" before adding it. That should get rid of the crash.
My guess is that a few moments later, it will be possible to create the sound. Perhaps OpenAL is just not ready when you're creating that sound.