I too am having the same issue. I've made 3 different enemies that shoot projectiles, and they work just fine. I made a new enemy, and it doesn't shoot projectiles. I have a sprite for the projectile, have a speed integer, "Is shooting" and "Uses Projectiles" are both checked. I made a test enemy that had with the same stuff put down and that too didn't work. Could I have too many projectile based enemies?