Plug-in disappeared after upgrade to 2.4.13

Hello,
I have just upgraded ALO EasyMail to 2.4.13 (French) on WP 3.4.2 (my web site : http://www.lecoledanslepre.com using Museum Core theme) and when I clicked on Bulletins menu to access to the plug-in settings, the message “Alors, on triche ?” was then displayed (instead of the plug-in page showing the list of newsletters managed). And the plug-in has disappeared from the interface. No way to get it back again in the left menu of WP interface! Checking the installed extensions, it is still listed as Installed.
Please help.
Kind regards,
Jean-Bernard

http://wordpress.org/extend/plugins/alo-easymail/