After updating your self-hosted WordPress.org website, when attempting to enter your administrative Dashboard you may get a Fatal error similar to this one:
Fatal error: Allowed memory size of 41943040 bytes exhausted (tried to allocate 30720 bytes) in … /wp-admin/includes/template.php on line 1604
For your situation, the path to the file, the filename, and the line number may be different. The memory numbers indicated may be different also.
There may be a variety of causes for this error.
One cause could be the WordPress JetPack plugin. Use an FTP program (or your host’s file manager) to remove or preferably move this plugin into a folder called “disabled.”
Then try entering your administrative Dashboard. The problem will most likely be resolved. However, the underlying issue hasn’t been fixed.
For a better solution, try increasing the available allotted memory for your WordPress installation. Edit your wp-config.php file. Be careful editing your wp-config.php file. Mistakes can result in your site not loading at all. Toward the end of the file, edit (or insert if needed) a memory statement so the file looks like this:
* Increase default memory.
/* That’s all, stop editing! Happy blogging. */
This includes a comment, and then a memory statement to allocate more memory.
Important Note: If you copy and paste the above into your editor, the single quote marks (‘) may be the wrong character set. Replace and type them manually.
Then restore the JetPack Plugin to its proper location (or reinstall it), and activate it. Now your admin Dashboard should work fine error free.