I wouldn't get upset with Cast Members on the dining reservation system. For one, the entire thing is in a flux right now. It was supposed to be up and available by October 21st and that ain't going to happen and was pushed back to November 21st. But who knows if that is going to happen. For two, for every call they receive from someone trying to make a reservation for dates they can't they have to explain the entire thing to them. And potentially have to deal with irate people about it. For three, I don't know of any business where every single employee gives the same answer to the same question. Even phone greetings differ most times. For four, I'm sure people would start to complain if Disney went to pat answers to all questions.
A Disney Cast Member is no different from anyone else answering phones in a company where a major computer system is not up and running at full capacity. They can only tell you what they know at that particular moment.
I always try and put myself into the other person's position and if I couldn't handle the job, then I don't really have a right to complain (which is why I hardly ever get that upset with restaurant servers).