It sounds like a problem with the Session ID you retrieved from Facebook.
Try re-authorising the Facebook account in WildFire. Ie, go to WildFire's Settings page, select the Facebook account from the list of Accounts setup, then press the 'Get Session' button. This should open a browser window to login to Facebook and approve WildFire. When you see a page with the word 'Success', copy the entire URL back into WildFire. When you click Apply it will extract the necessary information.