I had the same thing happen. I replaced the SLVoice binary in Singularity with the one from the official viewer (and copied over the necessary libraries). That fixed it for me.
I'm using Debian squeeze/testing and the 64-bit Linux client. I renamed the lib32 directory, and created a new lib32 directory with these libraries from the SL viewer for linux in the lib directory:
libortp.so libvivoxoal.so.1 libvivoxplatform.so libvivoxsdk.so
The rest of the dependencies were installed via apt-get and adding :i386