one line plugin not working

[Nullifi3d]

When I submit a new reply I get the following error:

Fatal error: Call to a member function on a non-object in /home/whd/public_html/includes/functions_newpost.php(427) : eval()'d code on line 1

I installed a plugin in newpost_complete. I tried 2 variations of the code:

$db->query("UPDATE user SET available = available + 100 WHERE userid = $bbuserinfo[userid]");

$db->query("UPDATE user SET available = available + 100 WHERE userid = $vbulletin->userinfo[userid]");