If you have just changed code (for example deployed a new module or moved an existing one) read http://drupal.org/documentation/rebuild
Additional uncaught exception thrown while handling exception.
Original

Twig_Error_Runtime: An exception has been thrown during the rendering of a template ("SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: INSERT INTO {watchdog} (uid, type, message, variables, severity, link, location, referer, hostname, timestamp) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8, :db_insert_placeholder_9); Array ( [:db_insert_placeholder_0] => 1 [:db_insert_placeholder_1] => php [:db_insert_placeholder_2] => %type: !message in %function (line %line of %file). [:db_insert_placeholder_3] => a:6:{s:5:"%type";s:7:"Warning";s:8:"!message";s:51:"PDOStatement::execute(): MySQL server has gone away";s:9:"%function";s:41:"Drupal\Core\Database\Statement->execute()";s:5:"%file";s:69:"C:\xampp\htdocs\drupal807\core\lib\Drupal\Core\Database\Statement.php";s:5:"%line";i:54;s:14:"severity_level";i:4;} [:db_insert_placeholder_4] => 4 [:db_insert_placeholder_5] => [:db_insert_placeholder_6] => http://localhost/drupal807/admin/people [:db_insert_placeholder_7] => http://localhost/drupal807/admin/structure/views [:db_insert_placeholder_8] => ::1 [:db_insert_placeholder_9] => 1391481746 ) ") in "core/themes/seven/templates/page.html.twig" at line 100. in Twig_Template->displayWithErrorHandling() (line 279 of C:\xampp\htdocs\drupal807\core\vendor\twig\twig\lib\Twig\Template.php).
Additional

Symfony\Component\DependencyInjection\Exception\RuntimeException: You have requested a synthetic service ("request"). The DIC does not know how to construct this service. in service_container_prod->getRequestService() (line 3283 of C:\xampp\htdocs\drupal807\sites\default\files\php\service_container\service_container_prod.php\a155ddbdc40b0fe421df7e92df51d6890201ee665734cf507cdec82d3bfd49e2.php).
Uncaught exception thrown in session handler.

Symfony\Component\DependencyInjection\Exception\RuntimeException: You have requested a synthetic service ("request"). The DIC does not know how to construct this service. in service_container_prod->getRequestService() (line 3283 of C:\xampp\htdocs\drupal807\sites\default\files\php\service_container\service_container_prod.php\a155ddbdc40b0fe421df7e92df51d6890201ee665734cf507cdec82d3bfd49e2.php).