Many Moodle users would like to use their PayPal account for purchases other than Moodle transactions. This is not possible since Moodle requires that the PayPal IPN be set within PayPal to return ALL purchase notifications to the Moodle server. If the PayPal account is used to purchase something other than a Moodle transaction, an IPN will be generated and sent to Moodle. Moodle will reject the IPN and evetually, after too many rejects/failures, PayPal will autmically turn off IPN all together.
What is needed is to include the PayPal notify_url (max characters 255) variable within the Moodle PayPal setup screen to be sent to PayPal along with the other purchase information. PayPal says to have Admins enable IPN on their PayPal account but to turn off notifications.