Redirecting to default.aspx page after forms authentication

Hi guys i am facing problem in forms authentication
In My application I have web.config file.
the authentication code is llike this

<configuration>
<system.web>
<authentication mode="Forms" >

<forms loginUrl="Login.aspx" name=".ASPXFORMSAUTH">

</forms>

</authentication>
<authorization>
<deny users="?"/>
</authorization>
</system.web>

<location path="Unsecure">
<system.web>
<authorization>
<allow users="*"/>
</authorization>
</system.web>
</location>

</configuration>

Under Solution Explorer

Unsecure :Folder
ForgotPassword.aspx

Root
Channel.aspx : this page is ->set as start up page
Login.aspx :Login button


on click of Login Button ->code goes here

FormsAuthentication.RedirectFromLoginPage(txtUserName.Text, false);

On click of Login Button and After successful authentication it redirect to Channel.aspx page.now i clicked on back button which takes me to Login.aspx page . here if i again wants to login then
it shows an error that default.aspx page not found
i tried to log in by entering values in textbox and clicked on Login button it shows Default.aspx page not founnd.
surprising, in my application ther is no default.aspx page.
what is the reason.what is missing in web.config file.

help is appreciated
PPCC

is this 2.0 or 1.1

its is framework 2.0

are you using the built in 2.0 controls.