Hello Roberto Pennacchia,
I am really sorry for the delay of this reply as it is a weekend for us here.
Based on your error message, it seems like when you configured the Facebook apps already deleted for Easyblog autoposting before.
Can you check your Facebook apps is it still existing in your Facebook apps store? If no, you have to create again with your Facebook apps and reconfigure the Easyblog Facebook autoposting setting in your site.
If you need further assistance, can you provide us with your Facebook account access, Joomla backend so we can help you reconfigure this for you? Please advise.