I had this problem earlier.   There are three G2 figures in a scene:  Sydney, Jessi and Simon.   It may be significant that they went into the scene in that order.   With the three of them and their various odds and ends, Poser was taking a fair amount of memory, but the saved file wasn't notably big on the hard drive.

  When I tried to render the scene all in one go, Poser gave up trying to render, but continued running, so I hid part of the scene and rendered the rest.   After that, Poser put out a message about being unable to load a texture, so I closed it and re-started it.   When I tried to open the scene, I was prompted to locate a file called 878628384.obj.   Since it was nowhere in the Poser folder, I had to take the option to give up the search.  

  The scene came up with Sydney and Jessi all present and correct, along with Simon's clothing - but no Simon.   I closed it without saving and tried opening a slightly earlier saved version.   This asked for the same mysterious .obj (or one with a similar nine-digit number, anyway), so I pointed it at the Simon geometry file.   Now everyone was in the scene, but Simon was unmorphed.

  I had a look at one of the saved Poser files and there were two references to 878628384.obj:

morphBinaryFile D:Program Filese frontierPoser 7RuntimelibrariesCharacterPoser 7SimonG2SimonG2.pmd
figureResFile C:DOCUME~1ABCDEF~1.ATHLOCALS~1TempPoser 7PoserUndoCache878628384.obj
actor BODY:10

  I have pretty much re-created the scene as it was, so I am not greatly bothered about repairing the old file, but I'd be interested to know what is causing the problem and how I can be confident of avoiding it, if anyone has any ideas, please.