Fundraising Paypal IPN problem - Not updating pledges automatically after a payment

Hello WPMU Team,

Yesterday I bought Fundraising which is a very wonderful plugin. I just finished to setup everything. But when I tryed to make a donation using both Paypal Sandbox and Live mode, nothing happens on the website. Except having this message after completing the transaction: "Oh No, we can't find your pledge. Sometimes it take a few moments for your Soutien to be logged. You can try refreshing this page"

All transactions are listed in the paypal transactions history of the "receiver" account, so I think the problem is from the IPN URL.