Sometimes your WordPress database will corrupt a table. Depending on your backup program, you may or may not be notified about it. The fix for a corrupt database table is pretty simple though.
Get into your Cpanel in your web hosting account. Find the database that your site is using. Check the box next to the table, and use the dropdown below the database to select repair table.
When its fnished, you will see a message displayed detailing the error and that it was fixed.