Most working – getting error on first button after PayPal

I am testing in Sandbox mode and have successfully tested the per day button but on the first button I’m having problems. The post with Pay Per View enabled can be found here:

I can get all the way through the PayPal processing and am returned to the page with a button that displays: “Confirm .99 USD payment to see this content”

When I click on the button, it displays the following error message:

Warning: Cannot modify header information – headers already sent by (output started at /home/uedcom/public_html/iwd/wp-content/plugins/pay-per-view/pay-per-view.php:176) in /home/uedcom/public_html/iwd/wp-includes/pluggable.php on line 881

Refresh just displays the same message but if I click the browser’s back button it shows the “hidden” content. I have tested this in IE9, Firefox, Chrome and Safari so it is not a browser issue.

NOTE: in IE 9 when I click on the link after clicking on the browser’s back button, a new tab opens rather than a new window with the video content. The new tab is the same page as the previous so the user doesn’t get access to the content they paid for.