Forms Authentication and Query Strings - .Net 4.0 iis 7

Hi,
I'm completely lost as how to resolve this issue, I'm not sure if it's occurring in iis or it's my .net
I have forms authentication and a login.aspx page using iis 7
I'm trying to achieve the following url:
http://localhost/foldername/login.aspx?id=7
but this keeps getting redirected back to
http://localhost/foldername/login.aspx
How do i resolve this issue?  I really need the id to be used as part of the login process
 
Thanks
 
Gemma 
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