WP_MEMORY_LIMIT option allows you to specify the maximum amount of memory that can be consumed by PHP. This setting may be necessary in the event you receive a message such as “Allowed memory size of xxxxxx bytes exhausted”.
This setting increases PHP Memory only for WordPress, not other applications WordPress will automatically check if PHP has been allocated less memory than the entered value before utilizing this function. For example, if PHP has been allocated 64MB, there is no need to set this value to 64M as WordPress will automatically use all 64MB if need be.
Please note, this setting may not work if your host does not allow for increasing the PHP memory limit–in that event, contact your host to increase the PHP memory limit. Also, note that many hosts set the PHP limit at 8MB.
Please check your PHP configuration before setup the maximum amount of memory
Add the following
define('WP_MEMORY_LIMIT', '64M');after
/** Absolute path to the WordPress directory. */
if ( !defined('ABSPATH') )
define('ABSPATH', dirname(__FILE__) . '/');
sources : WordPress Codex