Media Library gronked

While one of our authors was in the process of uploading images for a post, the Medial Library stopped working — to wit, there is now a new entry that shows the following in place of the most recent image:

Warning: strpos() expects parameter 1 to be string, object given in /home/lwa0002/public_html/wp-includes/post.php on line 188

Warning: preg_match() expects parameter 2 to be string, object given in /home/lwa0002/public_html/wp-includes/post.php on line 188

Catchable fatal error: Object of class WP_Error could not be converted to string in /home/lwa0002/public_html/wp-includes/post.php on line 189

All previous images in the library are visible. HOWEVER, it’s no longer possible to use the Insert Media function from within a post. We get nothing but a blank page on the Library tab.

From a visitor’s point of view, the site is working perfectly.

I’ve restored the database from several different backups. I’ve restored the file system from a recent backup. Nothing changes in terms of the Media Library error.

Any thoughts would be much appreciated.