I had this problem and I think the LibraryPrefs.xml had gotten messed up when I was editing it. Either I had a back up or I deleted it and let poser remake it. If you do that, you'll have to add all your external runtimes again

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Available on Amazon for the Kindle E-Reader Monster of the North and The Shimmering Mage

Today I break my own personal record for the number of days for being alive.
Check out my store here or my free stuff here
I use Poser 13 and win 10