create table test_varbinary_table(
    id int not null IDENTITY PRIMARY KEY ,
    name varchar(256) not null,
    rows int not null,
    cols int not null,
    vb_data varbinary(max) null
)

CREATE PROCEDURE insertData
    @name varchar(256),
    @rows int,
    @cols int,
    @data varbinary(max)
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    -- Insert statements for procedure here
    INSERT INTO test_varbinary_table
          (name, rows, cols, vb_data) VALUES (@name, @rows, @cols, @data);
END

double[,]  dblArySampleData = new double[2,3]  { {7.0, 3.0, 1.3 }, {8.333, 4.1211, 8.999 } };
    var result = new byte[6 * sizeof(double)];
    Buffer.BlockCopy(dblArySampleData, 0, result, 0, result.Length);

    try
    {
        using (SqlConnection conn = new SqlConnection(connString))
        {
            conn.Open();
            using (SqlCommand cmd = new SqlCommand("dbo.insertData", conn))
            {
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.AddWithValue("@name", "foo");
                cmd.Parameters.AddWithValue("@rows", 2);
                cmd.Parameters.AddWithValue("@cols", 3);

                cmd.Parameters.AddWithValue("@data", result);
                cmd.ExecuteNonQuery();
            }
            conn.Close();
        }
        textBox1.Text = "No Failure!";
    } catch (Exception ex)
    {
        textBox1.Text = "Error: " + ex.Message;
    }

try
    {
        using (SqlConnection conn = new SqlConnection(connString))
        {
            conn.Open();
            SqlDataReader rdrMatrix = null;
            DataTable tblMatrix = new DataTable();

            using (SqlCommand cmd = new SqlCommand("dbo.GetData", conn))
            {
                cmd.CommandType = CommandType.StoredProcedure;
                rdrMatrix = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                tblMatrix.Load(rdrMatrix);
                String strResult = "";
                foreach (DataRow dr in tblMatrix.Rows)
                {
                    byte[] retData = new byte[6 * sizeof(double)];
                    String retName;
                    retName = dr["name"].ToString();
                    strResult += retName + "rn";
                    retData = (byte[])dr["vb_data"];  // potential problem?
                    Buffer.BlockCopy(retData, 0, dary, 0, dary.Length); // potential problem?

                    for (int ri = 0; ri< 2; ri++)
                    {
                        strResult += "     ";
                        for (int ci = 0; ci<3; ci++)
                        {
                            strResult += " " + dary[ri,ci] ;
                        }
                        strResult += "rn";
                    }

                    strResult +=  "rn" ;
                }
                textBox1.Text = strResult;
            }
            conn.Close();
        }
        //textBox1.Text = "No Failure!";
    }

foo
0 0 0
0 0 0
bar
0 0 0
0 0 0