This could actually be a variety of things. The issue I had when I got this one was a networking issue. Open the Admin Console, on the General Tab of the Server Properties, in the Audio Settings, uncheck 'Use Default Audio Connection' and choose the IP you are using from the drop down. This solved my problem, but this could be a variety of issues, another thing I can think of of the top of my head is check your IIS permissions.
Michael Dunn
Senior Consultant
Microsoft Consulting Services
www.microsoft.com/services
612.859.1899
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