In playing with custom errors i found even though i set the <customerrors> and debug section in my web.config like those below
<error statusCode="403" redirect="NoAccess.htm"/>
<error statusCode="404" redirect="~/myerror.htm"/>
I found these settings were still getting ignored until i set the retail flag in the Machine.config.
…now i don’t know if this is a change with the .NET framework in Windows Server 2008 -or i had forgotten i had done this in the past but it is working this way now.