i have two Atrix 2 under 4.0.4 (rooted).
on one of them, i can capture screen-shots, on the other one, i cannot. so weird!
on the Atrix 2 that does not want to capture the screen, i see the message "Airdoid has been granted superuser privileges" flashing a couple of times when i try to capture the screen.
on the Atrix 2 where screen-capture works, i don't see this message flashing multiple times.strange!
note: I am able to get screen-captures fine with 3CX on the droid where i cannot get them with Airdroid.