During my last two aeroplan bookings, while doing the seemingly endless classic reward search dance, I encountered both of the errors mentioned . What worked for me was to be extremely patient, only fill in one field at a time and don't even attempt to move on to the next field until aeroplan fills in the field for you.
If the web site was fast and easy to use it might allow more people to book online without the aid of the call centre.
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I can just picture an AE executive meeting in action...
Customer relations exec: We're receiving numerous complaints that our website is buggy and useless.
IT exec: Exactly
Customer relations: What?!?
IT exec: We looking into spending money fixing the website and making it useful but all our analysis showed only downside to this course of action. You see, it would cost money to hire decent IT staff, cutting into our profits, cutting into our executive bonuses. Further if, the web site was useful, people would redeem travel rewards, which cost us money, which cuts into our profits, which cuts our executive bonuses. Of course, there are those that insist on booking travel rewards, as a means of discouraging this behavior, we charge them $30 to use our call centre; that on top of all other fees and charges we levy on travel greatly reduces the number of repeat users.
Customer relations: Wow, you're onto something there. Perhaps we should replace our call centre with a voice activated automated booking system -- fewer people required. We could even sell this as a benefit to our members as we could cut the call centre fee in half. And then, if the member insists on talking to an agent, we could increase the call centre charge.
IT exec: Exactly, and the best part is, you don't really need to spend all that much on an voice activated automated booking system as it only has to give the illusion of being useful. Remember, travel rewards are our single biggest cost.

