Binaryworld - Problem: Click Event not firing for ImageButton ... [ ASP.net -> General Errors ]

I had an Image Button with following properties in tag

<asp:imagebutton id="cmdSearch"
BorderWidth="1px"
BorderStyle="None"
BorderColor="Gray"
runat="server"
ImageUrl="images\general\search_a.gif"
ImageAlign="AbsMiddle"
CommandName="Search"
EnableViewState="True">
</asp:imagebutton>

I tried to write some code in following event but event didn't fire

Click here to copy the following block

Private Sub cmdSearch_Click(ByVal sender As System.Object, ByVal e As System.Web.UI.ImageClickEventArgs)
Response.Redirect("CodeListing.aspx?LanguageId=" & cmbLanguage.SelectedValue & "&SearchText=" & txtSearch.Text)
End Sub

then I changed my HTML code little bit and click event started working I dont understand this thing but its working perfact

Click here to copy the following block

And in code section

Click here to copy the following block

Protected Sub OnBtnClick(ByVal sender As System.Object, ByVal e As System.Web.UI.ImageClickEventArgs)
Response.Redirect("CodeListing.aspx?LanguageId=" & cmbLanguage.SelectedValue & "&SearchText=" & txtSearch.Text)
End Sub