I assume the same contents working fine with windows users, right? And is this issue unique to Lion or happend to older version of OS? Is there limited HW model to cause this problem or it's various models for Mac?
There are many hits with this google search: site:discussions.apple.com Lion no audio
Thank you for getting back to me. Yes, the lectures work fine for Windows users. The issue with the headset occurs with all versions of the Mac OS. The issue without the headset occurs only with Lion. This occurs on all Mac models. I've done a google search and the answers do not really apply to us. Because sound works for everything else except the lectures. I've tested using youtube videos and the audio plays just fine.
I asked Presenter team about this issue. They got to think two issues from this thread:
1) There is some known issue with USB headset specifically in Plantronics Blackwire 610M/620M with unplugging and plug it back.
2) The audio system is put to sleep on Mac Lion by some reason and need to refresh the page once or twice to make it work again. This issue happen with Presenter file but not other tools. (possible bug for Presenter)
I recommend to submit Presenter bug in this form: https://www.adobe.com/cfusion/mmform/index.cfm?name=wishform
Sorry but I don't think we can help for your issue from Flash Player side.
Thank you for getting back to me. The issue with the USB headset actually occurs with all types of headsets. I am actually in touch with someone in the Presenter department as well. I posted this problem here just in case this was also a flash player issue. Thank you for the link to bug site. I will use that in the future.