Attached Link: http://www.senosoft.com/

Some thumbnails have a broken alpha channel. I believe this can often be fixed by using P3DO Explorer (see attached link).

There is a free version and a paid for version (see RMP -> http://market.renderosity.com/mod/bcs/index.php?vendor=6261).
IIRC, the difference being the paid for version does bulk conversion, the free one only one at a time.