Here's what I did to solve it:
Open your existing smf.class.php 2.0.2a
Replace from line 1716 to 1772 the following code (function integratelogin):
function integrateLogin($user, $pass, $cookietime)
{
global $mainframe, $my, $database, $_VERSION, $mosConfig_lifetime;
global $modSettings, $context;
global $jsmfConfig;
$username = mosGetParam($_REQUEST, 'user', '');
$password = mosGetParam($_REQUEST, 'passwrd', '');
$cookieneverexp = mosGetParam($_REQUEST, 'cookieneverexp', '');
$cookielength = mosGetParam($_REQUEST, 'cookielength', '');
$remember = mosGetParam($_REQUEST, 'remember', '');
$jsmf =& jsmfFrontend::singleton();
$jsmf->doLogin(FALSE);
/* smf uses cookieneverexp set to on or cookielength equal to -1
* joomla uses cookielength equal to -1
* jsmf login uses cookielength equal to -1
* CB login uses remember equal to yes
* login is expecting 'yes' or 'no'
*
* the goal here is to identify all possible definitions of remember me
* and translate that to Joomla/SMF cookie never expire settings
*/
if (($cookielength == -1 || $cookielength == 525600 || $cookielength == 3153600 || strcasecmp($cookieneverexp, 'on') == 0) || (strcasecmp($remember, 'yes') == 0)) {
$remember = 'yes';
$_POST['remember'] = 'yes';
$modSettings['cookieTime'] = 3153600;
$context['never_expire'] = 1;
$cookieneverexp = 'on';
} else {
$modSettings['cookieTime'] = (int) $cookietime;
$mosConfig_lifetime = (int) $cookietime * 60;
}
if ($my->id <= 0) {
$query =
"SELECT password " .
"FROM #__users " .
"WHERE username = '$username'";
$database->setQuery($query);
$row = null;
$database->loadObject( $row );
$pass = $row->password;
unset($row, $query);
/*
* Mambo compatability
*/
if (strcasecmp($_VERSION->PRODUCT, 'Joomla!' ) == 0) {
$mainframe->login($username, $pass, $remember);
} else {
$mainframe->login($username, $pass);
}
}
return true;
}
With this new code from 2.0.2.1
function integrateLogin($user, $pass, $cookietime)
{
global $mainframe, $my, $database, $_VERSION, $mosConfig_lifetime;
global $modSettings, $context;
global $jsmfConfig;
$username = mosGetParam($_REQUEST, 'user', '');
$password = mosGetParam($_REQUEST, 'passwd', '');
$password2 = mosGetParam($_REQUEST, 'passwrd', '');
$password = ($password ? $password : $password2);
$cookieneverexp = mosGetParam($_REQUEST, 'cookieneverexp', '');
$cookielength = mosGetParam($_REQUEST, 'cookielength', '');
$remember = mosGetParam($_REQUEST, 'remember', '');
$jsmf =& jsmfFrontend::singleton();
$jsmf->doLogin(FALSE);
/* smf uses cookieneverexp set to on or cookielength equal to -1
* joomla uses cookielength equal to -1
* jsmf login uses cookielength equal to -1
* CB login uses remember equal to yes
* login is expecting 'yes' or 'no'
*
* the goal here is to identify all possible definitions of remember me
* and translate that to Joomla/SMF cookie never expire settings
*/
if (($cookielength == -1 || $cookielength == 525600 || $cookielength == 3153600 || strcasecmp($cookieneverexp, 'on') == 0) || (strcasecmp($remember, 'yes') == 0)) {
$remember = 'yes';
$_POST['remember'] = 'yes';
$modSettings['cookieTime'] = 3153600;
$context['never_expire'] = 1;
$cookieneverexp = 'on';
} else {
$modSettings['cookieTime'] = (int) $cookietime;
$mosConfig_lifetime = (int) $cookietime * 60;
}
if ($my->id <= 0) {
$query =
"SELECT password " .
"FROM #__users " .
"WHERE username = '$username'";
$database->setQuery($query);
$row = null;
$database->loadObject( $row );
if($_VERSION->DEV_LEVEL < 13) {
$password = $row->password;
}
unset($row, $query);
/*
* Mambo compatability
*/
if (strcasecmp($_VERSION->PRODUCT, 'Joomla!' ) == 0) {
$mainframe->login($username, $password, $remember);
} else {
$mainframe->login($username, $password);
}
}
return true;
}
This permit login with joomla 1.0.13 and fixes the broken reply message page.
I only tested it for a few minutes as my site was broken. Don't know if this is the perfect solution but seems it's working.
I hope Kevin will give us some details about it

Ciao