In reply to sharatk:
It seems that it is a simulator problem,
module sumExpt;
int arr[] = '{1, 2, 3, 4, 5, 6, 7, 8, 9, 3, 3, 3};
initial begin
$display("arr.sum(item) with ((item._index_ < 3) ? item : 0) = %0d", (arr.sum with ((item.index < 3) ? item : 0)));
end
endmodule
Hierarchical name component lookup failed at ‘index’.