get or post arguments causing `page not found` error in wordpress cutom template

I created custom template using this code,

<?php /* Template Name: npg */ 
  echo "hello";
?>

And assigned this template to new page, When i open that page i can see hello printed there.

Issue is, when i pass variable in get like this

http://lh/folder/pagename?s=123

Getting page not found error. But if i use like like this

http://lh/folder/pagename

I can see hello.

What is the issue?