How come when clicking to "Sign Up" for an upgraded account, it redirects to the home page

I've installed Membership Pro, and have gotten almost everything working the way I need it to. Where I'm having issues is that I've selected a payment gateway (PayPal) and a subscriptions page. When I go to the subscriptions page to go from Free to Full account status, instead of it returning /register-now/?action=registeruser&subscription=3, it's redirecting back to the home page. This site is still under development on a subdirectory of my site, hence the muddled URLs. Thanks!