Thumbnail Problem

I’ve been tearing my hair out trying to fix this problem. Anyone who can help me resolve it will have my eternal gratitude.

I’m using the Mayumi theme put out by Padd Solutions, which contains code to display a thumbnail next to the image post. See here for an example:

http://www.paddsolutions.com/wpmag/mayumi

However, I can’t seem to get the same functionality out of the theme with it installed on the website. The small thumbnails simply won’t load, despite them being perfectly available in the main post. Anyone know what’s going on and care to help? Here is the site and the problem, as you can see:

http://www.2girls1game.com

The first two posts are supposed to display the first image uploaded in the post. They don’t. The last two with thumbnails that actually work are pulling from the static thumbnail image because the posts don’t contain images.