WE HIGHLY SUGGEST USING THE GOOGLE CHROME EXTENSION TUTORIAL HERE
NEW FACEBOOK INVITE ALL CODE
Recently facebook changed its event invite system and in order to invite all your friends there is a new method :
Step 1 : Go to the event page you would like to invite all to (example : https://www.facebook.com/event.php?eid=138431042901754 )
Step 2 : Make sure you click "I'm Attending" and then Click on Invite Friends.
Step 3 : You have to now scroll down on your friends list until you reach the bottom, the new infrastructure facebook implimented only lists a certain # of friends at a time (lamesauce) so you gotta scroll down for a minute or two...