If the problem is with WordPress itself and some incompatibility with your Theme and not related to BPS in any way – We have seen this exact same problem with the Canvas Theme occur on a website.
If your Posts or Pages are not displaying on the WordPress Posts or Pages pages then you will need to upload the previous WordPress files for the previous version of WordPress you were using before you upgraded to WP 3.6. When you are prompted to update the database after you have uploaded all old WordPress files choose YES udate the database.
1. Download the WordPress version zip file from http://wordpress.org/download/release-archive/ to your computer.
2. Unzip the WordPress zip file on your computer.
Upload the entire /wp-content folder to your website.
Upload the entire /wp-admin folder to your website.
Upload the entire /wp-includes folder to your website.
Upload all the WordPress root files to your website root folder. There are somewhere around 17 WordPress root files. index.php, wp-activate.php, wp-app.php, wp-blog-header.php, etc.