Please make sure to check on these settings:
-To have the required access on themes files,
-check the execution time limit,change it on your server if not long enough to let all dummy data import.
-Check to have have enough memory limit.You can increase it yourself by adding this line into your wp-config.php file : define('WP_MEMORY_LIMIT', '94M');
Or ask your hosting provider to do it for you.
