Fatal error: Function name must be a string in ...

<?
    include("common.php");
    if( $_POST['username'] && $_POST['password'] ){
        $failed = 1;
        $username = $_POST['username'];
        $password = $_POST['password'];
        $query = "SELECT * FROM users WHERE username='$username' AND password='$password'";
        $result = mysql_query($query) or die ("Error in query: $query. " . mysql_error());
        if ( ($result) && (mysql_num_rows($result) > 0) ){
            $row = mysql_fetch_object($result);
            $adlogin = $row->username;
            $myname = $row->username;
            $adpassword = $row->password;
            $myuid = $row->uid;
            if ( ($username != $adlogin) || ($password != $adpassword) ){
                $failed = 1;
            }else{
                $failed = 0;
                $loggedin = 1;
                session_register("loggedin");
                session_register("myuid");
                session_register("myname");
            }
        }else{
            $failed = 1;
        }
    }
    if($loggedin){
        ob_start();
        header("Location: account.php");
    }
        include("header.php");
?><div style="float:left;"><img src="login.gif"></div><br /><strong>Einloggen :</strong><br /><br />
Hier gelangst Du in Dein Benutzer Zentrum.<br/ ><br />Du kannst Dein Forum verwalten und administrieren und zb Beiträge löschen usw. <br />
<br /><br /><br /><br /><form action="login.php" method="POST">
<input type="hidden" name="action" value="login"><font face="arial" size="2"><b>Username</b><br />
<input type=text name=username size=30 tabindex="1" maxlength="12">
</font><br>
<font face="arial" size="2"><br>
<b>Passwort</b><br>
<input type=password name=password size=30  maxlength="12">
</font><br>
<br>
<font face="arial" size="2"><input type="submit" name="" value="Login">
<br><br>
</font>
<font face="arial" size="2"><b><a href="mailto:<?=$adminemail?>?subject=<?=$sitename?>/Password"><b>Passwort vergessen?</b></a><br /></font>


<font face="arial" size="2"><b><a href="anmelden.php"><b>Neu anmelden!</b></a></font>


</form>


<?
    include("footer.php");
?>