I've seen a number of people have had this problem but I don't seem to be able to fix it.
I have installed at www.mamabridal.com/zenphoto
I'm on 1and1 as a host so have put the "AddType x-mapp-php5 .php" line in the htaccess file.
See below:

RewriteEngine Off

!!! Change this to the web path (eg: http://www.yourwebsite.com/photos --> /photos) !!!

RewriteBase /zenphoto

AddType x-mapp-php5 .php

RewriteRule ^admin/?$ zp-core/admin.php [R,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^.*$ - [R,L]

RewriteRule index.php$ index.php [L,QSA]
RewriteRule ^page/([0-9]+)/?$ index.php?page=$1 [L,QSA]
RewriteRule ^page/([A-Za-z0-9-_]+)/?$ index.php?p=$1 [L,QSA]
RewriteRule ^(.*)/page/([0-9]+)/?$ index.php?album=$1&page=$2 [L,QSA]

Rewrite rule addtion for search

RewriteRule ^page/([A-Za-z0-9-]+)/fields([0-9]+)/(.*)/([0-9]+)/?$ index.php?p=$1&searchfields=$2&words=$3&page=$4 [L,QSA]
RewriteRule ^page/([A-Za-z0-9-]+)/fields([0-9]+)/(.)/?$ index.php?p=$1&searchfields=$2&words=$3 [L,QSA]
RewriteRule ^page/([A-Za-z0-9-_]+)/archive/(.)/([0-9]+)/?$ index.php?p=$1&date=$2&page=$3 [L,QSA]
RewriteRule ^page/([A-Za-z0-9-]+)/archive/(.*)/?$ index.php?p=$1&date=$2 [L,QSA]
RewriteRule ^page/([A-Za-z0-9-]+)/tags/(.)/([0-9]+)/?$ index.php?p=$1&searchfields=4&words=$2&page=$3 [L,QSA]
RewriteRule ^page/([A-Za-z0-9-_]+)/tags/(.)/?$ index.php?p=$1&searchfields=4&words=$2 [L,QSA]
RewriteRule ^page/([A-Za-z0-9-]+)/(.*)/([0-9]+)/?$ index.php?p=$1&words=$2&page=$3 [L,QSA]
RewriteRule ^page/([A-Za-z0-9-]+)/(.*)/?$ index.php?p=$1&words=$2 [L,QSA]

RewriteRule ^(.)/image/(thumb|[0-9]{1,4})/([^/\]+)$ zp-core/i.php?a=$1&i=$3&s=$2 [L,QSA]
RewriteRule ^(.)/image/([^/\]+)$ zp-core/i.php?a=$1&i=$2 [L,QSA]

Catch-all - everything else gets handled in PHP for compatibility.

RewriteRule ^(.*)/?$ index.php?album=$1 [L,QSA]

As you will see if you go to www.mamabridal.com/zenphoto though the thumbnails and full images do not show. The images do show however if you click on the large image and see the full size one.

Anyone help?!?

the images are generating out of memory errors...

Fatal error: Out of memory (allocated 40632320) (tried to allocate 11648 bytes) in /homepages/7/d123417448/htdocs/mama/zenphoto/zp-core/functions-image.php on line 61

try using some smaller image files and see what happens

Thanks for that. I uploaded the image at a smaller size and all if fine now.

Good one! :-)