For some categories on my site there's introduction text that needs formatting (so using the category description isn't an option) and placing at the top of categories.php.

I've added a post ID to the category description field thinking I could then use get_post() to load the relevant post's content then list all the posts in the category underneath.

However it doesn't work and breaks the loop.

The error I get is

Fatal error: Only variables can be passed by reference in /wp-content/themes/pap_01/loop.php on line 39

and line 39 is

$secintro = get_post(439);
print_r($secintro);

I've tried resetting post data and rewinding the loop after this but nothing helps. And print_r($secintro); does show anything either.