I've installed IIRF for rewriting on a Windows server and the component Joosef (free version)
Now, if I activate the SEO on Joomla, I found this error:

Class 'SEFConfig' not found in D:\Inetpub\wwwroot\Hugnot_Joomla\Joomla\plugins\system\joomsef.php on line 39

What does it means and how could I get a solution?
Thanks a lot.
Donato