resource references fail

  resource "aws_vpc" "pdat" {
    cidr_block = "10.0.0.0/16"
  }

  resource "aws_security_group" "pdat_security_group" {
    name = "pdat_security_group"
    description = "pdat_security_group"
    vpc_id = "${aws_vpc.pdat.id}"

    ingress {
      from_port = 80
      to_port = 80
      protocol = "tcp"
      cidr_blocks = [
        "0.0.0.0/0"]
    }

    ingress {
      from_port = 443
      to_port = 443
      protocol = "tcp"
      cidr_blocks = [
        "0.0.0.0/0"]
    }

    ingress {
      from_port = 22
      to_port = 22
      protocol = "tcp"
      cidr_blocks = [
        "0.0.0.0/0"]
    }

    egress {
      from_port = 0
      to_port = 0
      protocol = "-1"
      cidr_blocks = [
        "0.0.0.0/0"]
    }

    tags {
      Name = "allow_all"
    }
  }