Authorize.net - checkout_failure

Greetings :-)

I'm having trouble with finalizing a cart that I've duplicated on numerous sites it the past with little trouble. I was using eCart v5.03, but just updated to v5.06 and am still getting the same errors on checkout click on the confirm.php page.

The ERROR:

Warning: Cannot modify header information - headers already sent by (output started at /home/public_html/confirm.php:18) in /home/public_html/confirm.php on line 391


The code from the confirm.php page

The site works great in TEST MODE with Authorize.net. This error only comes when it is in LIVE MODE.

I can confirm that the following is correct (As I have triple checked them already)

$AuthNet_required[0][$nextIndex] = "x_login";
$AuthNet_required[0][$nextIndex] = "x_tran_key";

$AuthNet_required[0][$nextIndex] = "x_test_request";
$AuthNet_required[1][$nextIndex] = "FALSE";

Thanks in advance for your assistance.

I figured it out. I had a stray space after a ?> in my php code on the confirm.php page.

Just took some effort to locate it.

Issue resolved.

for future reference, this thread talks about the possible causes and fixes for that error:
showthread.php?t=19285