For the broken images that appear when you're on the approval page after an upload, please try the fix posted in this thread:
http://www.vbadvanced.com/forum/show...6&postcount=15
It should show the /gallery/images/files_gif.gif image when there is not a thumbnail, so there shouldn't be any reason why you would get a broken thumbnail for those. If you'd like to submit a support ticket though I'll be glad to take a look and see what's causing that.