If you get this error message it usually means that Apache JMeter is not configured to output its results as XML, but instead is outputting them as CSV.
The default items to be saved can be defined in the jmeter.properties (or user.properties) file. The properties are used as the initial settings for the Listener Config pop-up, and are also used for the log file specified by the -l command-line flag (commonly used for non-GUI test runs).
To change the default format, find the following line in jmeter.properties:
jmeter.save.saveservice.output_format=csv and change it to:
For more details on configuring JMeter's output formats, please refer to: http://jmeter.apache.org/usermanual/listeners.html