As the title says, I can't put a bounty on 2 of the 3 AI.  The 3rd AI is my ally so naturally I don't want to put bounty on him.  The option is greyed out for the other 2 enemies...  I've seen this before when I've defeated an AI, but that I can't imagine that's the case here as I saw no message about it and one of the AI is certainly at least a little stronger than me (playing on cruel i think, the one above hard).

I searched for an answer but to no avail.  Any responses on what's going on would be greatly appreciated.  Thanks in advance.