"unkown sender" email confirmation

Hi, I just used events manager plugin, and try to book some event. but, the email confirmation which received by both event organizer and event user have a problem.

there is no email name sender, >> http://prntscr.com/2fsr49

I have set up it on email setting page, but it still not work >> http://prntscr.com/2fss6e

thanks

http://wordpress.org/plugins/events-manager/