Undefined index: force_ssl_login (no replies)

Hi,

Right now, when I login to my self hosted piwik installation I have a yellow background block of text like this :

There is an error. Please report the message (Piwik 2.1.0) and full backtrace in the Piwik forums (please do a Search first as it might have been reported already!).

Notice: Undefined index: force_ssl_login in /data/www/piwik/plugins/LoginLdap/Controller.php on line 753 

Backtrace -->

#0 Piwik\Error::errorHandler(...) called at [/data/www/piwik/plugins/LoginLdap/Controller.php:753]
#1 Piwik\Plugins\LoginLdap\Controller->checkForceSslLogin(...) called at [/data/www/piwik/plugins/LoginLdap/Controller.php:344]
#2 Piwik\Plugins\LoginLdap\Controller->login(...) called at [/data/www/piwik/plugins/LoginLdap/LoginLdap.php:95]
#3 Piwik\Plugins\LoginLdap\LoginLdap->noAccess(...) called at [:]
#4 call_user_func_array(...) called at [/data/www/piwik/core/EventDispatcher.php:98]
#5 Piwik\EventDispatcher->postEvent(...) called at [/data/www/piwik/core/Piwik.php:778]
#6 Piwik\Piwik::postEvent(...) called at [/data/www/piwik/core/FrontController.php:96]
#7 Piwik\FrontController->dispatch(...) called at [/data/www/piwik/core/dispatch.php:30]
#8 require_once(...) called at [/data/www/piwik/index.php:47]

OS : RedHat 5.4 x86_64
Apache : 2.2.22
Php : 5.3.7
MySql : 5.5.25
Piwik : 2.1.0 installed in a apache's vhost with LDAP plugin

Do you have any idea of the origin ?
Thanks