I think the reposting was acceptable because there was an error in the original posting, though it would have helped if the reposting had been to the same thread. Anyway, that is history now.
This type of problem is not very easy. There are two perfectly clear arguments.
 Partner knows I have three aces, since partner would not be making a slam try if he did not know that. Therefore, it being clear from his hesitation that he has one of the missing key-cards otherwise he would not be thinking about it, to bid a slam now is relying on the hesitation. This cannot be allowed, so it is automatic to rule it back to 5
 Partner may not know whether I have three or zero aces. While his hesitation shows this, so does the bidding. 5
asks me to go on with three aces, and pass with none. So it is permissible to bid 6
on the example hand, and we should allow 6
To be honest, I can see both arguments. Let see if we can find some more clues. In case  we are assuming that partner has something like
and he is worrying that I might have
which is ludicrous! Check the earlier bidding: you cannot be that weak!
No, Partner knows you must have an ace, case  makes no sense, and we can not allow the 6
So I would rule it back to 5