ASP.net Invalid URL redirect (C#)

I am using custom Errors tags to redirect to a page when ever an url is not found.

  <customErrors mode="On" redirectMode="ResponseRewrite">
  <error statusCode="404" redirect="error.aspx" />
</customErrors>

But the case is this

This is my page and the url is correct and it loads and works correctly. But whenever i type http://ift.tt/2paRqjl it dosent redirect to the error page neither it loads properly.

So i want it to redirect to the error page or remove that unwanted string from url and load the page correctly.

Can someone help me to get an idea how to do that ? thank you.