Hi Pasquale,
this has something to do how users are synchronized between MWS and IS.
In earlier versions (up to wM 9.12) it could be configured in MWS which JMS-Provider (DB or UM) should be used for this.
But from wM 10.x the option to configure it via UI has been removed.
The following Thread is dealing with a similar question:
This thread also contains a link to the online documentation.
Regards,
Holger