I've had something like that happen to me lots of times. The character (or characters) becomes invisible, but you can still see them in the hierachy editor. Since something similar frequently happens for me in Max I found out it was really a display problem. Or rater an OpenGL problem. Click the Maximize button (see the pic) and the character reappears. After that, you can restore the workspace to it's normal size again (you may need to temporarily detach the library palette if it was open because it'll cover the minimize button) (the solution in Max is the same btw. It forces a reload of the OpenGL screen)

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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.