Custom Errors in .NET

[C]

Hi,

I have an ASP.Net app.

I use <authentication mode="Windows" /> to detect if a
user has the rights to access certain pages.

If they do not have access they get an error stating
Access Denied 401.2 and I have a Custom Error Page for
this.

If the user does not have access a Windows Logon box is
displayed. If they enter their details 3 times they get
redirected to my Custom Error Page stating Access is
denied.

If they click on Cancel first the same error number is
diaplayed 401.2 Yet they do not get my custom error page.
They get the standard IIS Error Page.

If I try to log in 3 times I get Access Denied. If
subsequently click on Cancel during the same Session I get
my Custom Error Page.

However, if I click on Cancel first I do not get my custom
error page. Instead I get the IIS error page.

Any ideas ?

Here is the settings from my web.config

<authentication mode="Windows" />
<location path="secure/images">

<system.web>

<authorization>

<allow users="*" />

</authorization>

</system.web>

</location>

<location path="secure/include_files">

<system.web>

<authorization>

<allow users="*" />

</authorization>

</system.web>

</location>

<location path="secure/Defeasance.css">

<system.web>

<authorization>

<allow users="*" />

</authorization>

</system.web>

</location>

<location path="secure">

<system.web>

<authorization>

<allow users="mydomain\mylogin" />

<deny users="*" />

</authorization>

</system.web>

</location>

Thanks,
C.