this is the headers already sent error.
the important part of the error to note is:
output started at /home/costumff/public_html/product_view.php:1
this is telling you that the cause of the error is on the product_view.php page at line 1.
see the following thread for details on troubleshooting the headers already sent error:
in your case i think the issue is The Unicode Signature (BOM) PHP bug described at the end of that post.