Can't attack custom NPC

[Didokon]

Hi, I've recently downloaded the 3.5.5a Eternion WoW repack, and when today I added a custom boss to it, I can't attack him when I spawn him.
He attacks fine, scale is fine, etc, but I just can't hit him.
Anyone knows why?
Thanks

[DoxramosPS]

I would say check flags and faction to start in your Database.

[stoneharry]

Collision issues. Vmaps for that area do not exist yet the server is trying to use them. Make sure you have fully generated them or disable collision in the world config.