HTTP error when uploading files

1) Add this to your .htaccess file at the root of your WordPress installation just before the # BEGIN WordPress line:

SetEnv MAGICK_THREAD_LIMIT 1

OR

2) add this to your themes functions.php file (actually add to a child theme functions.php file or use a plugin likeCode Snippets )

add_filter( 'wp_image_editors', 'change_graphic_lib' );

function change_graphic_lib($array) {
return array( 'WP_Image_Editor_GD', 'WP_Image_Editor_Imagick' );
}