Error with CRON after updating to 4.7.6
I discovered I had an issue with Joomla's database.  Here is the answer I found:
The fix is easy:


Enter your Joomla site's backend
Select from the admin menu: Extensions -> Manage -> Database
Click on the FIX button. You may find that some other updates need to be done to bring the database up to 3.5.
Head to Global Configuration, and turn the site 'off' before this next step to discourage any users for a while.
Then, as mentioned above, head to phpMyAdmin and delete all the entries in the xxxxx_sessions table.
Head to the backend and turn the site back on.


http://forum.joomla.org/viewtopic.php?f=710&amp;t=913838