How can i see native code?

[C# Programming]

Hi, i would like to explain my problem. I want to see the code when my applcation generate an exception.
I create a simple application that crash when a button is pressed:

private void button1_Click(object sender, EventArgs e)
{
Int32 Text;
Object obj= null;

Text= (Int32)obj;
}

This code generate a NullReferenceException when it try to make a cast of "obj".
Now, i run .exe file on a pc with only VS2008,when i click the button,jitdebugger start and ask me where is the file .cs.
My questions are:
Why the jitdebugger ask me where is the .cs file?
If i open module page (ctrl+alt+u) i see my file .exe with symbols loaded, but i can see the c# code.
Help me please.
Thank you, have a nice day
bye bye