First, try not to use offensive comments and words, because they will be first edited, and if you continue, will grant you a ban on the forum. BTW, welcome to the forum, and to your first post...
First, before saying "I have *exactly* the same problem", it must be checked if this is really the case. Missing buildings is the effect, not the cause. The effect might looks the same, but the causes might be many.
Even in this thread, there were two posts which SEEMS to be "similar", but in fact they are entirely different, because one said buildings disappeared after some minutes, which simply indicates everything's working, but the scenery was still not activated but, since the user never came back to report, we'll never know for sure.
So, the first question is: do you have BOTH the "Addon Manager" AND the "Couatl powered products" under the FSX "Addons" menu ?