How to create a strong name key(snk) for mulitiple references dll in n-tier ASP.net application?

Hi All,
Can anyone please tell me how to create a snk for all existing dlls(multiple) in n-tier ASP.net application?
I have created a asp.net application using n-tier. My web layer contain refrences of all layers(data,facade,core,common).but when I try to create strong key of web layer it throws error as "refrences assembliy can not have Strong name".
Thanks in advance.
Cheers!
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