I'm playing single-player, first time through on the easy settings, and I'm at the final mission where I have to kill the 4 cloaked Ceph. I might have stumbled onto a bug, because I simply can't kill these guys. I have tried every weapon available to me at that point (K-volt,shotgun,special forces scarab, C4, JAW). I've also ran into a terrain glitch where the cloaked Ceph were right in front of me but could not hurt me. And I shot at them until I ran out of ammo, but they never died. (Actually, I've exhausted my ammo on several attempts - these guys just won't die - arrrrgh!!!!)
I would appreciate if anybody could help me here.