Can't access control ID in code behind

I have the following code in my aspx page: ``` <asp:Button runat="server" ID="myButton" Text="hello" /> ``` and this in my code behind: ``` protected void Page_Load(object sender, EventArgs e) { myButton.Text = "bye"; } ``` For some reason the intellisense picks up the "myButton" id in the code behind but when it compiles it says it can't build because it doesn't recognise it! My page is a default aspx page which uses a master page, the button is inside a content control and all is set to run at server correctly, the page runs and displays fine except for this button resolution issue! Any ideas?