Problem upgrading 2.6 to 2.7 -

I'm currently getting the following errors when attempting to upgrade from Moodle 2.6 to 2.7

Warning: array_fill(): Number of elements must be positive in Drive:\htdocs\moodle27\lib\dml\mysqli_native_moodle_database.php on line 1245

Warning: implode(): Invalid arguments passed in Drive:\htdocs\moodle27\lib\dml\mysqli_native_moodle_database.php on line 1245

The corresponding error in php.err is:

Exception ignored in shutdown function array (
  0 =>
  tool_log\log\manager::__set_state(array(
     'readers' =>
    array (
      'logstore_standard' =>
      logstore_standard\log\store::__set_state(array(
         'logguests' => '1',
         'manager' => NULL,
         'component' => 'logstore_standard',
         'store' => '',
         'buffer' =>
        array (
        ),
         'buffersize' => '50',
         'count' => 0,
      )),
    ),
     'writers' =>
    array (
      'logstore_standard' =>
      logstore_standard\log\store::__set_state(array(
         'logguests' => '1',
         'manager' => NULL,
         'component' => 'logstore_standard',
         'store' => '',
         'buffer' =>
        array (
        ),
         'buffersize' => '50',
         'count' => 0,
      )),
    ),
     'stores' =>
    array (
      'logstore_standard' =>
      logstore_standard\log\store::__set_state(array(
         'logguests' => '1',
         'manager' => NULL,
         'component' => 'logstore_standard',
         'store' => '',
         'buffer' =>
        array (
        ),
         'buffersize' => '50',
         'count' => 0,
      )),
    ),
  )),
  1 => 'dispose',
):Error writing to database

Is this an error with config.php or something else?