title: illegal characters at line 1 and col 1 in xml response in jmeter
body: <p>I am trying to validate the xml response from an REST API using JMETER. I am using xml schema assertion to validate the response using xsd. </p>
  
  <p>I am getting the following error on XML Schema Assertion </p>
  
  <pre><code>Assertion error: true
  Assertion failure: false
  Assertion failure message: fatal: line=1 col=1 Content is not allowed in prolog.
  </code></pre>
  
  <p>When i see the response that i have received i see there are some illegal characters that is added at the beginning of the response xml.</p>
  
  <p><a href="https://i.stack.imgur.com/MGpZm.jpg" rel="nofollow noreferrer">enter image description here</a></p>
  
  <p>I have tried to modify jmeter.properties file and changed the following values</p>
  
  <pre><code>jmeter.save.saveservice.output_format=xml
  jmeter.save.saveservice.data_type=true
  jmeter.save.saveservice.label=true
  jmeter.save.saveservice.response_code=true
  jmeter.save.saveservice.successful=true
  jmeter.save.saveservice.thread_name=true
  </code></pre>
  
  <p>Please help me in understanding how to remove the illegal characters in the response and allow the xsd validation to pass through.</p>