Facebook sharing unavailable with AddThis tool

We've been getting people who can't share article pages using the AddThis tool. The error says:

This content is no longer available
The content you requested cannot be displayed right now. It may be temporarily unavailable, the link you clicked on may have expired, or you may not have permission to view this page.

This has been happening for at least the past few days, but it could have been even earlier than that. Has anyone else seen this error?