Control Not Found in Javascript Method while callling a javascript method through ScriptManager in Codebehind

[Brijendra Kumar]

Dear Sir/Madam,

I am in a problem.
I have a javascript method and calling this method from codebehind, but object is not found whenever
i am calling this javascript method client side then it working fine.
Code is as follows:

Javascript:

function Test()
{
var a =  $find('<%=ComboBox1.ClientID%>').get_value();
alert(a);
}


protected void btn_click(object sender, EventArgs e)
{
  ScriptManager.RegisterClientScriptBlock(Page, Page.GetType(), "script", "Test();", true);
}


Please solve............

Thanks & Regards
Brijendra Pandey