This error renders when a script exceeds the default memory_limit setting inside your PHP configuration file(php.ini) on your server. Best practice is to always make more efficient programs instead of maxing out the PHP memory limited allocated. If you must allow a beefy memory hog file to run you can check the fix suggestions below. You may have to restart Apache to have any php.ini changes take place, especially on local PHP environments.

How can i fix it

Adjust your php.ini file memory_limit setting to something higher using this line:

memory_limit = 20M 

Or use the ini_set() php function directly in the script that is exceeding default memory limits. Example:

ini_set("memory_limit","20M");