IIS 7 need to replace symbol in url for asmx call

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IIS7

ASP.NET

IIS

WCF

webservice

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I need a specific requirement to replace symbols in a URL at IIS 7 / Virtual directory

ASMX call : http://XXXXXXXXXX%3Fquerystring%3D43 (example)

The url gives an error 'potentially dangerous request was detected from the client' and unable to change the source of this url

so, whenever this asmx call reaches to IIS, need to replace symbol below like this and redirect it.

%3F into ?
%3D into =

Please guide me how to do that.