It is odd texture sizes in versions of Blitz3d before v1.88 that is causing the errors on the Geforce 6xxx cards. It was discussed in these 2 topics a little while back.
http://www.blitzbasic.com/Community/posts.php?topic=52325
http://www.blitzbasic.com/Community/posts.php?topic=52904
http://www.blitzbasic.com/Community/posts.php?topic=52325
http://www.blitzbasic.com/Community/posts.php?topic=52904