Oh well thanks all for your help I really appriciate your prompt reply.
I have fixed the problem and if someone else is having the same problem here's what to do. This will resolve the unread thread and login problem both.
just coment out or delete the following from you modules/Your_Account/index.php file.
Code:
if (is_user($user)) {
$uinfo = getusrinfo($user);
$lv = time();
$db->sql_query("UPDATE ".$user_prefix."_users SET user_lastvisit='$lv' WHERE user_id='".$uinfo['user_id']."'");
}