Check with your ISP to find out if PHP has been upgraded lately. The latest php releases whine about all sorts of things that were OK before.
Please note that all of the output has been Warning: messages. These might or might not be important, but you can probably get back to a functioning site pretty quickly.
You can suppress Warning messages in php.ini, .htaccess or index.php Check with your ISP on which is appropriate for your situation.
It's also possible that you have turned on error reporting in one of your other plugins (that's what happened to me).
Bottom line: you can turn those errors off if you want.
Google search on "php warnings suppress"