Instant Payment Notifications
If you're having trouble with the PayPal Standard Secure add-on, one of the first things you can try is to enable Instant Payment Notifications (IPN).
To do this, you would need to log in to your PayPal account and go to Profile and Settings and then the My Selling Tools page.
On the My Selling Tools page, find the Instant Payment Notifications section and click Update.
If you have never set up your IPN information before, you will need to select the Choose IPN Settings button.
On the next page, you will enter the URL for your IPN and ensure that Receive IPN messages is enabled.
Your IPN URL will be your domain followed by /?it_exchange_paypal-standard-secure=1
Payment Data Transfer
You can also try enabling the Payment Data Transfer (PDT) option.
To do this, go back to your My Selling Tools page and click the Update link for Website Preferences.
Find the Payment Data Transfer section and insure that the option is set to on.