title: The proxy server received an invalid response from an upstream server in odoo
body: <p>While generating the Reports under payroll module in local odoo server - I am getting the following error:</p>
  
  <pre><code>Odoo
  
  XmlHttpRequestError Proxy Error
  
  &lt;!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"&gt;
  &lt;html&gt;&lt;head&gt;
  &lt;title&gt;502 Proxy Error&lt;/title&gt;
  &lt;/head&gt;&lt;body&gt;
  &lt;h1&gt;Proxy Error&lt;/h1&gt;
  &lt;p&gt;The proxy server received an invalid
  response from an upstream server.&lt;br /&gt;
  The proxy server could not handle the request &lt;em&gt;&lt;a href="/web/dataset/call_button"&gt;POST&amp;nbsp;/web/dataset/call_button&lt;/a&gt;&lt;/em&gt;.&lt;p&gt;
  Reason: &lt;strong&gt;Error reading from remote server&lt;/strong&gt;&lt;/p&gt;&lt;/p&gt;
  &lt;hr&gt;
  &lt;address&gt;Apache/2.4.7 (Ubuntu) Server at 192.168.111.188 Port 80&lt;/address&gt;
  &lt;/body&gt;&lt;/html&gt;
  </code></pre>