Large group IMs are not initating when a large number of people are ruining the First Look Voice client. It's causing the session to time out before it starts. You can see it trying to populate the top part with all the names of the people running voice before it eventuall times out.
"Error starting a new chat session with Second Life Mentor. Error making request, please try again later."
This is easlily reproduced by joining a large group where the majority of people are running the Voice Cient such as Second Life Mentor. Try to start a session using either client when a lot of people are on.
Submitted Bug rt.lindenlab.com #894359