title: NSURLErrorDomain error codes description
body: <p>This is my first experience of developing an ios app. I am trying to Post some data using Facebook graph api. I am constantly getting the following error:</p>
  
  <pre><code>The operation couldn’t be completed. (NSURLErrorDomain error 400.)
  </code></pre>
  
  <p>I cannot able to find the description of NSURLErrorDomain error codes. What does the 400 error code means ?</p>