1) Can’t log into the admin
This may happen if at one time changes were made to your Photo Cart files because if server sessions issues or login issues. You will need to implement a work around as described here:
http://www.picturespro.com/faq/index.php?faq=21

 

2) Broken thumbnail links on the customer side
This means you have the $setup[‘url’] wrong in your setup.php file (which is in the Photo Cart folder).
It should look like:

$setup['url'] = "http://".$_SERVER['HTTP_HOST']."/photocart";
 OR
$setup['url'] = "http://mywebsitename.com/photocart";

You may have something other than photo cart, but it must not have a / at the end.