Rhino had some bugs with obj files.  Win XP problems were fixed in 3c. VistaPro exports from macs also crashed. The current  service release is Sr5b. If you turned off the updater try downloading the latest from the website. All previous updates are included.

AS: I picked up the mesh exported from Poser 6 with Rhino and only grabbed one object, but when I tried again just now to explode it said" exploding 13 meshes into 27." I was running my egg render in Bryce and didn't want to stop it. sorry.