FacebookOAuthException: Error validating access token on WP7 using Facebook C# SDK

I have a strange problem with the Facebook C# SDK on Windows Phone 7. I am using the SDK to post pictures to开发者_StackOverflow社区 users' walls. For the first authentication and the first few posts, it works great. After a while (I have a feeling the magic cutoff is 24hrs) I start to get an error on every post:

FacebookOAuthException was unhandled

(OAuthException) Error validating access token.

This happens after my line of code that does the actual post has run...

m_facebook.PostAsync(@"/photos", parameters, PostComplete);

... but before my PostComplete callback function is called. No code of mine is running when the exception happens. My Application_UnhandledException is not called - I get the error in a dialog in the middle of the screen in VS, and it says that no source code is available.

If this exception means I need to show the login screen again, that's fine - right now I'm both not sure what it means and not sure how to trap the bugger. Any help appreciated.

Chris

What publishing permissions do you use?

By default, access tokens expire after a short time period to ensure applications only make requests on behalf of the user when the are actively using the application.

For getting a long-lived access token, you need to ask for the offline_access permission.