UE4 crash on macbook air (on start up)

i have my macbook air. i have got this game before and i did not have this problem the reason i got rid of it was of.

  1. i had to get rid of like four games just to get it.
  2. the other is that when i got into a game it would just lag vary bad and i did not like it so i got rid of it.

i do not know if you are just having some problems and you are down for mac like i see the other guy with the pro.
is there something we need to do???