If you look at the source code for page two of your gallery, it looks like its dying before it even gets to Plogger. In fact, it dies before finishing the rendering of your subnavigation. Do you have any other dynamic code embedded in your page?
If you want, you can change "Number of Thumbnails per Page" to a higher value in the options menu and the second page will disappear. This is at least a temporary solution until you can figure out what is killing your site.
It bombs in the admin interface now . I couldn't change it to show 50, so I deleted image #20 until the problem occurs on the album page with 20 showing. Therefore, it looks like I need to delete pic 20 in that album, but how?
Try deleting the image from your /plogger/images/ directory using FTP. The entry should appear in your admin as an empty box, and you should be able to delete safely.
If that doesn't work, you need to go into the database and delete the entry by hand. Look in the plogger_pictures table for the correct row to delete.