Error: Data structure returned is not convertible in the requested format: Only integer keys supported for array columns on base level. Unsupported string 'Africa' found for row 'array ( 'Africa/Algiers' => 'Algeria', 'Africa/Luanda' => 'Angola', 'Africa/Porto-Novo' => 'Benin', 'Africa/Gaborone' => 'Botswana', 'Africa/Ouagadougou' => 'Burkina Faso', 'Africa/Bujumbura' => 'Burundi', 'Africa/Douala' => 'Cameroon', 'Atlantic/Cape_Verde' => 'Cape Verde', 'Africa/Bangui' => 'Central African Republic', 'Africa/Ndjamena' => 'Chad', 'Indian/Comoro' => 'Comoros', 'Africa/Brazzaville' => 'Congo - Brazzaville', 'Africa/Kinshasa' => 'Congo - Kinshasa - Kins'. Try to call this method with the parameters '&format=original&serialize=1'; you will get the original php data structure serialized.