"Why should I have to buy it again, I've already paid my subscription.?"

You shouldn't, and if the previous suggestion doesn't help, I would request technical support from the Ancestry staff.

Is this happening every single time you attempt to access the images, or only on occasion? The reason I ask is that I subscribe to the US census images too, and when I use Ranked Search, sometimes census records from England are mingled in. If I'm not careful, I end up trying to access images I don't subscribe to. LOL...

Good luck!
Lee