Membership2 and PayPal Single Gateway not working


Having just switch payment methods from Paypal Standard to PayPal Single Gateway, I have discovered that Paypal is not talking back to the membership website and thus membership is not given to the buyer.

I had the membership payment working with the Paypal standard gateway and then the client decided to switch from recurring payments, and thus the gateway was switched to the single gateway.

Payment is taken and the user is taken back to the membership site, but the user is not added to the membership.

Any ideas? Is an IPN needed?