This is the way you're suppose to be able to download the SD version of an HD purchase. However, for a few months now, I have not been able to do this. I've always been able to do it before, but for some reason, it stopped working. I contacted Apple, of course, this is not something that any phone advisor will know about because they are not knowledgable of the product, they just read off the same articles we can see online here, so they don't even know what I'm talking about when I mention this to them, and if you email iTunes Support, they're just quick to give you a refund without actually attempting to resolve the issue. Anyway, someone else mentioned that if you just click on the price of the SD version, you're asked if you want to buy it again, and someone else said you're asked if you want to download. I have seen both happen, and I'm not sure which happens when, but just earlier today, I was successful in clicking on the SD price of 2 movies and was only asked to download them again, and successfully downloaded the SD versions. This is something that is a problem with iTunes itself, not with anyone's specific Apple IDs or computer or anything else, it's just an issue with iTunes that Apple probably is not even concerned with fixing. In the meantime, you'll just have to keep finding alternatives. One way or another, I've found a way around it, such as these options, but also downloading the SD versions on my iPhone and Transferring Purchases.