Fatal error: Out of memory errors

I am getting these errors randomly since I moved my WordPress installation from my development server to the live server of a client of mine. My client’s previous website was created in Joomla and I have removed those files and as far as I know just copied the WordPress files from my dev server to the active server and created a new database. Anyway WordPress is working fine except for these error messages.

First I check the host’s php settings and memory limit is set to 512M

I then inserted define( ‘WP_MEMORY_LIMIT’, ’64M’ ); in the wp-config.php right after define(‘ABSPATH’, dirname(__FILE__) . ‘/’);

I tried changing the values of the memory limit in the wp-config.php.

Nothing works and I keep getting these error messages at random.

Do any of you have further tips?