I had the same problem, and the answer is a bit complicated....

Here's how to fix the problem with Lightbox alone:
See post #792 here for the fix:
http://www.zen-cart.com/forum/showth...=45314&page=80

If you use Lightbox AND Image Handler 2 together, you need to do the fix above. In addition you need to use the fix below:
See post #986 here for the fix:
http://www.zen-cart.com/forum/showth...=35913&page=99

One last thing.... This is optional, it fixes something I consider a nuisance, but additional images still work without this fix:
I'm not sure exactly under what conditions this happens, but I know that I have this problem with Lightbox, IH2, and a bunch of other mods installed. On IE browsers, if I have two additional images, the images don't line up on the bottom in one row. This is caused because with IE browsers 100% width just doesn't seem to work right here. For 3 images, no problem because 33%+33%+33%=99%. For 1 image, no problem, because it is only one additional image. With 2 additional images, 50%+50%=100% -- PROBLEM!!! So, I changed the following in modules/additional_images.php:

// List Box array generation:
if ($col_width == '50') {
$list_box_contents[$row][$col] = array('params' => 'class="additionalImages centeredContent back"' . ' ' . 'style="width:49.99%;"',
'text' => "\n " . $link);
} else {
$list_box_contents[$row][$col] = array('params' => 'class="additionalImages centeredContent back"' . ' ' . 'style="width:' . $col_width . '%;"',
'text' => "\n " . $link); }
$col ++;
if ($col > (IMAGES_AUTO_ADDED -1)) {
$col = 0;
$row ++;

Of course, if you change the number of additional images per row from 3 to another number, this fix would need to be modified. 4 wouldn't work because 25+25+25+25=100!

I hope that helps. :)