How to redirect to Error Page when authorization is invalid?

Hi Sir,

I have a problem with my project. 
My Problem is: If a non administrator tries to access the Admin section, he should be redirected to an error page : "ErrorPage.aspx". 
I have created "ErrorPage.aspx"
But, in my Program, Unauthenticated (Non Admin) user is redirected to Login Page: "SimpleUserLoginAfterRegistration.aspx".

Kindly Help me

Below are contents of Web.config of Root Folder:

<authentication mode="Forms">
<forms loginUrl="SimpleUserLoginAfterRegistration.aspx" defaultUrl="InnerPage.aspx" timeout="100" slidingExpiration="true" cookieless="UseCookies">
</forms>
        </authentication>
        <authorization>
            <allow users="*"/>
        </authorization>

And Here is the Webconfig settings in Administrator/Web.config :

<?xml version="1.0"?>
<configuration>
    <system.web>
      <authorization>
        <allow roles="Administrator"/>
        <deny roles="Manager"/>
        <deny roles="User" />
      </authorization>
    </system.web>
</configuration>

Kindly Help.....