There can be only one page directive - Error

Hi, i got the error 
Error 18 There can be only one 'page' directive..(apsx.cs file - header-)
And i really don't know what the problem is, i tried everything plz help if you can.
This is the code line.
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Header.aspx.cs" Inherits="Header" %>