Hi, I am not sure why it would be freezing and sending you back to the desktop when starting that mission. How long has this been occurring? I would suggest making sure all your drivers are up-to-date and fully restart your computer & router again before playing.
^hopefully this is helpful, but if the problem still occurs, I would suggest speaking with Official Activision Support via live chat whenever you get a chance. They should be online in about 1.5 hours.