Just a note: I've seen this happen when Poser gets confused and thinks an object doesn't have any material zones. The object will load, its geometry will load, but because there are no materials present and, for some reason, Poser has allowed that to happen, the object will not be rendered in the Preview or Render pane - There are no materials to render.

This has happened to me when either Poser borks up for whatever unknown reason that "borkup_code_764" was loaded for or Poser has to scramble for memory and has decided, arbitrarily, to ditch references for fussy things, like material zones. (Typically, in the latter case, everything goes black, first. Then, things start to "disappear", usually whatever information I forgot to save. :) )

Given what Poser has to deal with, sometimes, this is, admittedly, a rare thing and not reliably reproducible. On imports, I see it most when I've been fussing with an object and cause the problem, myself, using external software.

As detailed above, the most common cause is a CR2 (or other similar file format) loading with geometry reference errors.