omprising the Procedure Call.</li>
      <li>The target procedure does not exist on the server. For HTTP GET, a server SHOULD
            use <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.5">404 (Not
                Found)</a> instead of 500.</li>
      <li>The procedure could not be invoked due to an error resulting from <a href="#CallApproximation">
            call approximation</a>.</li>
      <li>The invocation took place but resulted in an error from inside the procedure. </l