I remember hearing about this problem, I can't remember the solution though :o( A search here might bring up something. I do believe it's codec-related. You have the latest Servicepack (4.1), right?

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.