Lisa,
This is a known problem. We have reported it at:
http://tracker.moodle.org/browse/MDL-32387
Please go their and vote to get it fixed. I cn not beleive this is not fixed yet. Paypal worked great in Moodle 1.9. In later versions it was made part of the core and has not wroked proplery since.
Please vote to get it fixed. The Paypal feature today does not work properly at all when it comes to re-enrolling. It did before.
Doug