Think i resolved this issue…
Might be a problem with other classes loaded by the gallery or by Google.
Had the same problem with AJAX pagination script vs lightbox. And i found this solution on a forum.
You have to add this part of code to kpg.class.php at line 319 and 324.
onclick='myLightbox.start(this); return false;'
Will look like print <a href='$fullURL' onclick='myLightbox.start(this); return false;' rel='lightbox[kpicasa_gallery]'></a>
Works for me