I'm guessing this is because I (wrongly) used a couple of short PHP tags within the qa-facebook-login.php file. These work almost everywhere but can be disabled in a PHP configuration. So please go through qa-facebook-login.php, and find where there is a PHP open tag <? without the word php immediately after it. If it's <?= then replace it with:
If it's just <? then replace with:
Please let me know if this fixes that problem.