Joey Ricketts on "HTTP Error when trying to upload certain images."

Add this to your theme's function.php file.

add_filter( 'wp_image_editors', 'change_graphic_lib' );

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

That has typically worked for just about every other user that I've seen.