Two things that have worked for me when I get a scene "stuck" with the material room crash:

1.  Open the scene, move something in the preview window.  Select a light.  Use the advanced materials properties button on the properties palette to guide you into the material room.  Make your changes and save.

2.  Open a new scene, import your stuck scene.

3.  The problem seems to generate from the GUI.  Save a good UI memory dot.  Make sure the dot is selected before going into the material room.  (haven't had a crash since I've been doing that faithfully.... but it is random, so I don't have high hopes.)

For one fleeting second once I saw an error from Poser before the crash that Poser was unable to read the .pmd file.   Doesn't make any sense since I think the problem with the GUI, but I don't pretend to know much.  :)

Indi.