Solution:
This issue can have several causes. Since the problem is not permanent, it’s likely related to a network or MySQL issue.
To fix it, try repairing the database by following Step 3 from the tutorial:
1. dd the following line to your wp-config.php file:
define('WP_ALLOW_REPAIR', true);2. Visit: http://www.yoursite.com/wp-admin/maint/repair.php
3. Follow the on-screen instructions as outlined in the tutorial.