For the past weekend I've been trying to connect to modern warfare on pc. Im playing from Shanghai China. I couldn't connect once because of this error. I emailed support and they couldn't help me. Today I got home and turned on my astrill vpn. Selected "tunnel applications" option in settings and now my game connects.
Take note Activision your network routes from china to your Asia server are *****ed. I just solved your problem hit me up if you have job opportunities at Activision. For the rest of the world.