Relying on indexed fields in MySQL queries is not reliable and not compatible with all MySQL installations. The fix is simple.
diff --git a/extensions/Cargo/CargoUtils.php b/extensions/Cargo/CargoUtils.php index 78e4979..56b7ab2 100755 --- a/extensions/Cargo/CargoUtils.php +++ b/extensions/Cargo/CargoUtils.php @@ -123,7 +123,7 @@ class CargoUtils { $dbw = wfGetDB( DB_MASTER ); $res = $dbw->select( 'cargo_tables', 'main_table' ); while ( $row = $dbw->fetchRow( $res ) ) { - $tableNames[] = $row[0]; + $tableNames[] = $row['main_table']; } return $tableNames; }