Same here. I’m the admin of the page I publish to and everything worked fine until today. Plugin published correctly since I installed it a while back and every day for the past week. Today I get the same error as mtschirs:
Facebook returned an unexpected error: (#240) Requires a valid user is specified (either via the session or via the API parameter for specifying the user.
Try to resolve this issue, update the plugin or inform the author about the problem.
[Error occured at line 347]
I checked the plugin settings and everything is configured correctly…nothing was changed from the initial setting.