If you see an error that looks like this:
Warning: require_once(/xxx/xxx/xxx/assets/smarty/Smarty.class.php): failed to open stream: No such file or directory in /xxx/xxx/xxx/assets/includes/initialize.php on line 155
The root of the error is a case sensitive issue. The file "Smarty.class.php" should have a capital S but the file on your system is "smarty.class.php". For whatever reason your FTP, or perhaps the server extraction process put the file on the system with a lower case s. There are a lot of files in the photostore 4 package that are case sensitive and must have the capital letters.
To correct this issue, you will need to FTP all the files from the store package (EXCEPT for the /assets/includes/db.config.php file) to your store and make sure the case sensitive files are uploaded correctly.
You may also want to contact your hosting provider and tell them to remove anything they have installed that wants to control the case sensitivity of a files name.
For example going to: http://www.--your--domain--.com/assets/smarty/Smarty.class.php should not redirect you to http://www.--your--domain--.com/assets/smarty/smarty.class.php (it shouldn't change the capital S to a lowercase s).