Button Control Error

Hi Friends,
    I am havig Error like this in buton control event.
CS1061: 'ASP.main_registrationmaintab_add_ascx' does not contain a definition for 'Imgbtn100_Click' and no extension method 'Imgbtn100_Click' accepting a first argument of type 'ASP.main_registrationmaintab_add_ascx' could be found (are you missing a using directive or an assembly reference?)
Design page code:
<asp:ImageButton ID="Imgbtn100" runat="server"
ImageUrl ="~/images/Knob Add.png" onclick="Imgbtn100_Click" />
Code-behind Page:
protected void Imgbtn100_Click(object sender, ImageClickEventArgs e)
{
this.Panel4.Visible = true;
}
Can any one resolve this problem.
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