s2member blocking admin-post.php

I’m using s2member in conjunction with WP Event Organiser for a site. I’ve had another custom plugin built to track whether users attended events they signed up for – the user logs in and is presented with a list of their bookings – they answer yes or no to each. This works fine if the user is an admin, but if the user is a mere subscriber, they’re redirected to the login welcome page.

The custom plugin author reports that he thinks this behaviour could be because s2member is blocking access to

/wp-admin/admin-post.php

. Does anyone know if this is the case? If so, is there a way to change that behaviour?

Many thanks in anticipation!