My idea would be to try saving one item at a time until you hit the bad obj. I believe Carrara uses about 30 MB per Poser figure when imported as facet meshes, but it might be 60 MB (or more) per figure when imported as vertex object. So even 1 GB might not be enough to handle (and save) the entire scene as vertex objects, especially if you're using some of those big 3000X3000 Poser textures, saved internally. There is also a known bug where Carrara renames Poser materials as lists of numbers upon saving, but I don't know if that applies to you.