I keep getting the same error on multiple past posts on wordpress. Tried all the previous solutions given below, ie., clear error messages and delete existing facebook link. Didn’t work for me, but may work for you.
E19 How can I remove error messages?
The first thing you should try is to simply update the post(s) using the WordPress update button. The plugin will add a link to the post if it didn’t already do that and remove the error message in the process. You can also tick the checkbox Clear error messages in the post submit box, near the update button. In this way you can clear the error message without adding a link to Facebook (you’ll probably want to check Do not add link to Facebook too in this case). Since version 1.163 you can clear all errors for the current user using an option in the settings tab ‘Misc’.
U09 How can I add a link to an existing post?
Change the post status temporarily to draft, update the post and publish the post again.
