Hi Tom,
I am sorry for the delay of this reply.
Regarding your issue, my bad. EasyBlog 3.9.x slightly different from EasyBlog 5.0.x. To fix your issue, you need to login to your facebook ( your personal account that you used to authenticate FB in EasyBlog ) and go to your Facebook settings -> apps and delete the app name that you've created for your EasyBlog. See the example here:
http://screencast.com/t/xF64MFZ0KS .
Once you've delete app settings from your facebook, now go back to your EasyBlog backend under facebook autoposting and click on 'revoke' button to re-authenticate facebook in your EasyBlog
Hope this help and have a nice day!