How can i get the referer link when a user shown a page not found

The redirect is likely due to a difference in the web.config. In particular, check the system.web/customErrors and system.webServer/httpErrors nodes, which should be as follows:

<customErrors mode="RemoteOnly" redirectMode="ResponseRewrite" defaultRedirect="~/error.aspx">
	<error statusCode="404" redirect="~/utility/error-notfound" />
</customErrors>

<httpErrors errorMode="DetailedLocalOnly" defaultResponseMode="ExecuteURL">
	<clear />
	<!--If you run your application under a virtual directory, update this value to reflect it  eg:/myAppName/utility/error-notfound-->
	<error statusCode="404" path="/utility/error-notfound" responseMode="ExecuteURL" />
</httpErrors>

Turns out our web.config got modified for some mysterious reason