WE took our family to Aruba to our marriott vacation club last year, however this year, I was unable to get the dates that I wanted even though, I tried booking 9 months ahead. So I decided to trade my 3 bdr week; the first thing the booking agent asks is "do you want to deposit your week?" So, I said yes, or else I could not have searched for anything . Then, he said, I can't get another 3 bdr anywhere, so I am "out" one of my bedrooms. This doesn't seem exactly right, so be careful.
Intersting....when you called II did you get to the marriott Owners' Desk? If so, did they help you with "request first" vs. "exchange first"?
In either case you still need to have a week booked somewhere as opposed to banking then exchanging. We've done this several times and have great success getting where we wanted. The unfortunate thing is you're looking for ARuba which is second in popularity only to Hawaii.
One trick you could consider for the future is to try and "trade" a week you've booked with an Aruba owner who is looking for a week in your property. Just a thought....
I own a 3 bedroom at a different resort and have learned that when exchanging at resorts that have comparable or less bedrooms, the strategy is to go for 2 villas, a 2 bedroom plus a 2 bedroom or studio. The Marriott Desk at II is trained to accomodate 3 bedroom owners. The second and smaller villa is provided at a very steep discount for the length of your stay.