Thanks for writing in!
Cornerstone is a required plugin when using xtheme, even if you are not using it, it needs to be installed and activated for the theme to work correctly.
Try to increase your
memory limit and
maximum execution time by adding the code below in your
define( 'WP_MEMORY_LIMIT', '256M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );
Please add it before this line
/* That's all, stop editing! Happy blogging. */
Hope that helps