You said the Damper moved? Is your crank pinned?
If it's not, I almost guarantee that you spun the hub on the crank and it backed out. This would either,
1) Spin the crank on the hub and it would walk the belt off and shred it.
2) Stop the belt completely and the inertia of the sudden stop would shred it.
If not that then, did you install the spacer on the pensioner for the accessory belt?