Emoncms base on Synology, can't start service-runner, fail at step USER

I have a new installation of emon ^cms base on my synology, it works fine.
But I try to install service-runner, and I can0t make it work.

I change the service-runner.service with this config:
[Service]
User=www-data

Reload the systemctl deamon
systemctl daemon-reload
systemctl restart service-runner.service

But still getting the error:
Sep 14 13:55:22 EmonCMS systemd[1138633]: service-runner.service: Failed to determine user credentials: No such process
Sep 14 13:55:22 EmonCMS systemd[1138633]: service-runner.service: Failed at step USER spawning /usr/bin/python3: No such process
Sep 14 13:55:22 EmonCMS systemd[1]: service-runner.service: Main process exited, code=exited, status=217/USER
Sep 14 13:55:22 EmonCMS systemd[1]: service-runner.service: Failed with result ‘exit-code’.

Any help welcome!
Arno