Working with old version of Mcreator, 1.5.9. How can I fix the crash upon spawning mobs?

To start, I never moved past Minecraft 1.7.10 because none of my favorite mods did. Working with Mcreator 1.5.9 to make a mod for MC 1.7.10.

I made an item that shoots a dispenser fireball when used. However, the game crashes whenever I use the item, stating something like "unable to cast EntityFireball to EntityLiving". I think it's just an error in the code that Mcreator spits out. Does anybody have any ideas on how to fix this?