Label1 doesn't exist in current context

Question

Hi

 

this code gives the error "Label1 doesn't exist in current context":

 

aspx-code

<asp:Button ID="Button1" runat="server" />
<asp:Label ID="Label1" runat="server" ></asp:Label><br />

code-behind:

partial class oop : System.Web.UI.Page
{
protected void Button1_Click(object sender, System.EventArgs e)
{
Label1.Text = "ok";
}
}

Thanks for help.