There is a limit to the number of thumbnails you can have in a library - not sure what it is in Poser 6 offhand. If the missing thumbs are only in the most densely populated library folders, it might be that. Second, if you generate your own thumbs by saving, you'll miss out on any information that was in the real thumbnail. Things like MAT poses won't work after re-saving because they're hacked, not a native Poser file: in fact anything hacked is likely to break. But really, anything you've bought should have thumbnails with it - if not, then basic marketplace quality control has failed. Check that the product is listed as suitable for Mac. If you've had to run it through Macconvertor, there may be issues (but I'm not an expert there). Ask the vendor - they should be able to help.