While trying to used the hue Web Ui I've had the same problem. I my case the problem was that the impala service was not running. I was trying to do a hive query but impala was set as the default application. So as soon as I connect to Hue Web Ui it tries to connect to the Impala server and throws the error message. Therefore any query you run gets executed by impala and throws the error. To solve this, you must check that impala service is running properly.
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