Yeah, it looks like it was too late. I ended up using hook_nodeapi and everything seems to be working fine.

Date: Tue, 23 Mar 2010 22:27:08 +1000 From: "Lee Rowlands" <leerowlands@rowlands-bcs.com> Subject: Re: [development] Using drupal_access_denied() To: <development@drupal.org> Message-ID: <000501caca84$290afc00$7b20f400$@com> Content-Type: text/plain;       charset="us-ascii"

Hi, By the time you get to preprocess_page it's probably too late for drupal_access_denied, for the same reasons as drupal_add_js doesn't work in preprocess_page functions (see http://www.drupaler.co.uk/blog/joys-preprocessing/70), perhaps you might need to use hook_menu_alter instead and override the access callback? Lee

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If I do:

function mymodule_preprocess_page(&$vars) {  if ($some_condition) {    drupal_access_denied();    exit;  } }

I just get a white page (which is a 403 page looking at the header, not a 500).