On the new maxx, you only can add guests to calendar invites with the gmail calendar selected. Any other calendar, including my corporate exchange calendar, you can not add guests. Lakes with both Verizon and Motorola, and no one knew why. Totally ridiculous.
I got around this by downloading the google calendar app from the play store. Set up your exchange account on it and you can invite guests. I then deleted the stock calendar shortcut from my home screen and replaced it with the google calendar shortcut. It's not ideal, but it works.