No thumbnail found

Using the latest version of wordpress and this plugin.

I have some 4000 posts on my wordpress blog, every entry is a youtube video.

Every entry is laid out in the iframe way of showing a youtube video. I’ve scanned all posts for thumbnails, yet it can only fi nd about 150 thumbnails for 4000 entries of videos. Each time it says “No thumbnail found”

Any help?

http://wordpress.org/extend/plugins/video-thumbnails/