Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($function) must be a valid callback, first array member is not a valid class name or object in /homepages/21/d466042668/htdocs/app466042601/wp-content/plugins/jetpack/class.jetpack-sync.php:65
Stack trace:
#0 /homepages/21/d466042668/htdocs/app466042601/wp-content/plugins/jetpack/modules/post-by-email.php(21): Jetpack_Sync::sync_options('/homepages/21/d...', 'large_size_w', 'large_size_h', 'thumbnail_size_...', 'thumbnail_size_...', 'medium_size_w', 'medium_size_h')
#1 /homepages/21/d466042668/htdocs/app466042601/wp-content/plugins/jetpack/class.jetpack.php(611): require('/homepages/21/d...')
#2 /homepages/21/d466042668/htdocs/app466042601/wp-includes/class-wp-hook.php(287): Jetpack::load_modules('')
#3 /homepages/21/d466042668/htdocs/app466042601/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(NULL, Array)
#4 /homepages/21/d466042668/htdocs/app466042601/wp-includes/plugin.php(484): WP_Hook->do_action(Array)
#5 /homepages/21/d466042668/htdocs/app466042601/wp-settings.php(420): do_action('plugins_loaded')
#6 /homepages/21/d466042668/htdocs/app466042601/wp-config.php(319): require_once('/homepages/21/d...')
#7 /homepages/21/d466042668/htdocs/app466042601/wp-load.php(37): require_once('/homepages/21/d...')
#8 /homepages/21/d466042668/htdocs/app466042601/wp-blog-header.php(13): require_once('/homepages/21/d...')
#9 /homepages/21/d466042668/htdocs/app466042601/index.php(17): require('/homepages/21/d...')
#10 {main}
thrown in /homepages/21/d466042668/htdocs/app466042601/wp-content/plugins/jetpack/class.jetpack-sync.php on line 65