Maybe I'm slow, but it actually took me a few times before I realized that i could click on the different radio buttons.
This may be because the selected one just looks a bit different from what we're traditionally used to. Do you have options?
Something where the selected one is more solid and looking more like a selected button would probably help.
Of course, maybe I'm the only one that had this experience. Just thought I'd mention it in case it's more than just me.