To get the correct answer to this problem, we need look no further than problem 3, where you were going to protect partner in balancing seat with a double in case he was trapping. At IMPs, however, I'm a 2S bidder, since game is still possible, while not probable. I'll take my plus, and also, the spade bidder may balance, in which case I can make an optional double. Either 3H or 2NT could be right. I'll go with 2NT because it's more flexible.
Aces seem to play better in suits.
They're also good for defense, Mark. 2NT with only one spade stop is not too attractive. Partner can always give me 3S when 3NT is going to be right. Partner's hand wasn't provided, but I wish it had been for this one. I gave 3NT and 4NT both the highest score.