I get the following error when I publish a post on a sub-blog
Catchable fatal error: Object of class WP_Error could not be converted to string in /home/xxxx/public_html/mydomain.com/wp-includes/post.php on line 4356
The post is published on the sub-blog but it does not show up on the tags blog (or the tags blog RSS feed).
I am running BuddyPress on the site as well. The tags blog is using the Genesis News theme.
I get the same error on all sub-blogs regardless of the theme. If deactivate Sitewide tags I do not get the error.
I am running super cache as well as testing a bunch (its a development site) of wpmudev plugins (their global tags and post indexer are deactivated - they were active).