He just sits in the first floor of the bloodsucker lair aiming his rifle at the elevator door. Call of pripyat is a good game but these bugs are killing the game.

http://imgur.com/tdLQe9o < < < < How to make him moooooove!!!!

ok, I found the fix. Just change the switch distance inside alife.ltx to 150 and the quest will run with no problem.

NPCs often freak out like that in Stalker games. Sometimes just running around killing everything they want dead can get them going again.