Are you using high-quality textures? If so, sometimes Poser runs out of memory when loading these - try disabling bump maps or substituting the textures with some reduced-size ones (be sure to "save as", close poser and then re-open it with the new textures, however). Also, should you be using some old MAT files for P4, they sometimes load .bum files as bump maps, which are rather huge if hi-res (and AFAIK do nothing on P5) that can be removed at once.