Ilias,
The datafeed logger is for sending data from VXML Server to the Reporting Server.
 
If you haven't configured the Reporting Server through the Ops Console and haven't associated the VXML Server with a Call Server, and haven't configured the VxmlServer to send data to the Reporting Server in the Ops Console, then you'll get errors.
You should either configure the above information (if you're using the Reporting Server) or you should modify the STudio app and remove the DataFeedLogger (Project /Properties/ Call Studio/ General - in the Loggers box, highlight and Remove the DataFeedLogger.  This way, the system won't try to send data to your Reporting Server.
 
Janine