Try to open the file in a text editor and see how it looks. If it looks like a Poser scene it MAY be recoverable. I don't know anythng about macs but can you change the file extension to whatever a Poser scene file have on a mac and see what happens?

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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.