Today (Jan 28, 2013) the PayPal IPN stopped working in mine and several other stores which are using my PayPal module. The customer can go to PayPal and make the payment. But PayPal is not posting back to update the orders in Miva Merchant. Until the issue can be resolved, I suggest you go to admin > global settings > search on paypalr on the right. Click Edit button. Uncheck the Active box. Click the Update button.