Problems when members don't complete the subscription step

Latest Membership Plugin, Latest WP.MU.

I've had a member who completed the first step of the subscription (username, name, password, email, etc) but did not complete the second step (paypal).

This caused their account to deactivate.

They then contacted me saying they couldn't get into the site, and I don't have an easy solution. What instructions do I need to follow when this happens please. I am hoping it is really simple, and I am just missing something.

The site is http://photographyprojects.co.uk

Thanks for your help.