This works well.
When transferring data from object[,] to double[,] - use copy method &
specify length of the array.
In this case it is 4 (2 rows, 2 columns)

See the code below for example.

object[,] data = new object[2,2];
data[0,0] = 0.5d;
data[0,1] = 1.5d;
data[1,0] = 2.0d;
data[1,1] = 5.5d;

double[,] ddata = new double[2,2];
Array.Copy(data, ddata, 4);
Console.WriteLine("ok");
ddata[0,0] = 3.5;

Console.WriteLine(ddata[0,0]);
Console.WriteLine(ddata[0,1]);
Console.WriteLine(ddata[1,0]);
Console.WriteLine(ddata[1,1]);

HTH
Kalpesh