Infinite loop begin play using beam

Hello there. I 've made a beam which can be blocked by a cube which I spawn. If i spawn the cube 620 units or less closer to the start point of the beam(screenshot3), the BP crashes and event begin play returns infinite loop.I have no idea what 's goin on. Any ideas?

alt text If the cube collides with the beam I set the beam and the collision from start point of beam to the cube.