If you are using the W3 Total Cache plugin on your site then do the following to make it work with Simple Membership Plugin.
- Go to the “Page Cache” menu from W3 Total Cache admin menu. It is the 3rd menu item in the main W3 Total Cache admin menu.
- Scroll down to the “Advanced” section.
- Add the following line in the “Rejected Cookies” field.
You should also exclude the membership login page from caching.