I got the same error for dbx 3.1.4 for splunk 7.1.4 and splunk 6.6.11 in Windows. I installed the brand new splunk and copy paste my old splunk_app_db_connect folder to the splunk/etc/apps/ to 'install' the app. I restart splunk and got the same error message.
My solution is to refresh the Settings under Configuration tab in dbx app. You may need to change the JRE Installation Path by one letter and change it back. Then you click the save on the right. The task server will restart. After a few seconds, it will say task server restart successfully. Then you are ready to go! I didn't change any of the setting but just trigger the refresh task server.
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