Yep, this happens quite often. I am in a modified DADT, so I try to schedule things around my wife's schedule. Sometimes this works, often times not. But even when I DO tell her ahead of time it doesn't always work. Like Halloween this year, and the unexpected visit home from college of my youngest. I ended up changing plans because my wife was excited and wanted family time. (Amongst other things)
I think Pat makes a great observation. I would add of course that because many wives don't care for CDING and view it with disdain, they see it as the bottom priority. Sometimes they will even sabotage the effort if they are mad enough.
Unfortunately you will find that when this happens, you can't go back and say, "well, what about all the times I had to sacrifice". That goes over like a lead balloon.
Tina, I feel for you, but unfortunately, some time we just have to sick it up, and move on. Hopefully there will be another opportunity just around the corner. Otherwise, you may have to make your own opportunity with a weekend away, by your self.