Membership Not Connecting to Paypal

I am using paypal via a number of plugins (marketpress, events manager, fundraising, membership), and they all work except for membership. I disabled everything and still can't figure out what the issue is. I set up and disabled the IPN in paypal. The link membership is sending is:

domain.com/register/?action=registeruser&subscription=1

But this just returns the user to the homepage.

Do I need the IPN set up? What if I am using other paypal connections via fundraising and marketpress?

Alternatively, should I try using Protected Content Plugin instead?