Cannot modify header information

inf_user.php:
<?
require_once("backend/functions.php");
//require_once("themes/NB-TSpy/block.php");
dbconn();

loggedinonly();
?>[...]

functions.php: 
function dbconn($autoclean = false) {
	global $mysql_host, $mysql_user, $mysql_pass, $mysql_db, $THEME, $LANGUAGE, $site_config;

	if (!ob_get_level()) {
		if (extension_loaded('zlib') && !ini_get('zlib.output_compression'))
			ob_start('ob_gzhandler');
		else
			ob_start();
	}

	header("Content-Type: text/html;charset=$site_config[CHARSET]");

	if (!function_exists("mysql_connect"))
		die("MySQL support not available.");

    if (!@mysql_connect($mysql_host, $mysql_user, $mysql_pass))
    {
      die('DATABASE: mysql_connect: ' . mysql_error());
    }
     mysql_select_db($mysql_db)
        or die('DATABASE: mysql_select_db: ' . mysql_error());

	unset($mysql_pass); //security

    userlogin(); //Get user info	

	//Get language and theme