Affiliates - users aren't being added to my system

Hi suuport

I'm trying to get the Affiliates plugin to work so my users can help to promote my site and get paid.

I've tested this several times by switching to another user and signing up to the affiliate scheme, however users aren't being added to my system when I check my affiliate users in my admin screen - not one single signup according to the stats!

I've got the membership add-on enabled as it's a membership site too...