Trying to secure pages I've added -- getting error

Hi, I have added pages to a CMS I've created via PowerCMS, and I am now trying to ensure that these pages are secure, but I am getting an error:

Warning: Cannot modify header information - headers already sent by (output started at /Users/username/Sites/website/admin_cms/tbl_news_Detail.php:10) in /Users/username/Sites/website/WA_SecurityAssist/Helper_PHP.php on line 65

Basically, I have copied the code from a secure page created by PowerCMS:

<?require_once( "../WA_SecurityAssist/Helper_PHP.php" );?>
<?php
if (!WA_Auth_RulePasses("Administrator")){
WA_Auth_RestrictAccess("users_login.php");
}
?>

and pasted it into the relevant pages, but I am getting the afore mentioned error.

I have also tried running the Security Assist Access Pages Manager, but for some reason, the wizard affected the whole of the admin section (including untouched by me PowerCMS pages) and ended up breaking the code to the PowerCMS protected pages... they stopped working entirely.

Any thoughts?

the error happens if there is output on the page between php tags.

the error is reporting the problem around 10:
output started at /Users/username/Sites/website/admin_cms/tbl_news_Detail.php:10

see this thread for details on the cause of the error and troubleshooting steps:
showthread.php?t=19285

I had a shed load of line spaces from where I'd copied lines and pasted!

Thank you.