error in usercontrol codebehind controls

I am working with UserControl file that is mypage.ascx and mypage.ascx.vb files.
mypage.ascx page consist two text boxes named 'username' and 'password' and i am wishing to use these text boxes in its code behind file that is in mypage.ascx.vb. Here my codes goes:-
mypage.ascx

Username<br /> <asp:TextBox ID="username" runat="server" Width="120px" Font-Names="Verdana" Font-Size="11px"></asp:TextBox> <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ErrorMessage="Username can't be empty." ControlToValidate="username" ForeColor="Red">*</asp:RequiredFieldValidator> <br /> Password<br /><asp:TextBox ID="pa ...