Collision problem

Maybe you did call ResetEntityon the enemy after the first detection? Or you did hide him, or even free him or something? You could use CountCollisions to check if the enemy was hit one or two times. Additionaly I'd suggest to use polygonal collision.

BTW instead of EntityCollided you may use somethin like

For i=1 to countcollisions(shot)
 impact=collisionentity(shot,i)
 if impact=enemy then do something
next