What puzzles me is that there's grey behind it. Usually when the library won't show due to firewalls or anything else, it has a lighter background there.

Have you changed ANY settings lately? Updated firewall or antivirus?
Did Windows do an update?

Since it has been there, something must have changed outside of

Poser to make it go away. 

Do you get any error messages when Poser starts?

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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.