Thumbnail display problem using Lightbox2 with LemonTwist theme

Issue Summary

I have installed BG on Drupal 6.22 and it works great except for the block display of thumbnail images, which is one of the reasons I picked it in the first place. My thumbnails are set to display in 3 columns in the right hand block. Two of the three columns display an image but the leftmost column is always populated with black boxes. The borders also display abnormally and some of the images over run the border. The links do work, however, and the full size images display properly in Lightbox2. I found that if I changed the theme from LemonTwist to Marvin, it seemed to display the thumbnails properly, but I don't know what I need to change to fix this. Is it the theme, the module, or a configuration change that I can make myself? I'm not expert enough to figure this out, so any assistance would be much appreciated. Thank you. (please see attached screen image for example; site is at www.portablesawmill.ca )