Some time back I had a issue loging in to my wordpress admin panel it throwed me error message. I found solution from WordPress Forum. This is bcos of memory leakage of some plug-in. I will show how to fix this issue.
Login to your website backend and cd to your wordpress home directory and then append the below lines save and close the file.
# cd /var/www/html/website/wp-admin/includes
# vim /var/www/html/website/wp-admin/includes/wp-config.php
/** The custom WordPress Memory Limit. */
Now access your WP-ADMIN without any error message.