UPDATE:
it was a problem with the settings on Facebook. I just deleted the iOS app settings and everything worked.
I've implemented ShareKit with my iOS app without any trouble. Followed all the steps of the installation, including the SSO part for Facebook.
When pressing the Share button, I can send as email or tweet. Facebook worked once and now it stops. I authorized the app the first time and was able to share. I then removed the authorization from Facebook and when pressing the button on Sharekit, it says "saving to Facebook", switches to the Facebook app, and then back to my app with the "There was an error while authorizing" message.
I tried with two different Facebook accounts. any idea where to look for problems?
Thanks