Why has my Facebook access token suddenly stopped working? "OAuthException: Error validating access token."

I have an iframe Facebook application that uses the Facebook PHP SDK to authenticate and make api calls. During authentication, the user is prompted for Basic Info and Offline Access. If they allow my app access, Facebook redirects them back to my app and provides a session array, which contains access_token and an expires value of 0. At this point I save this session array to the database, and on subsequent pages, I fetch it and pass it to $facebook->setSession(). After that I make api calls. Everything was working fine last night for me, then this morning when I refreshed my browser, I get this Exception: OAuthException: Error validating access开发者_运维技巧 token.

I've also tried not passing the session array, and instead passing the access token directly to $facebook->api() but I get the same error. From what I understand, this access token should always be valid because of the offline access permission that was granted. Any ideas why this would suddenly stop working?

This could be caused by an issue that Facebook was having with access tokens. The issue was solved a few hours ago. See more details here: http://developers.facebook.com/live_status