ClientScript.RegisterClientScriptBlock not rendering output when called from Button_Click

Question

I have a Button_Click event ultimately calling ClientScript.RegisterClientScriptBlock, yet when the button is clicked and the source of the response is viewed - no script block has been outputted to the stream.

Is there any obvious reasons why this could happen?

I will provide further info if needed.

Cheers

INFO
Nothing AJAX just vanilla post-backs.
example:

protected void buttonSubmit_Click(object sender, EventArgs e)
{
  ...
  Page.ClientScript.RegisterClientScriptBlock(typeof(GetHeadHunted), "AnalyticsTrackingCode", output);
}