Your using the command “update-rc.d wdmcserverd disable”. If so the system response you received appears to be normal. Its the same output that I receive when running that command.
Conversely if one runs: /etc/init.d/wdmcserverd stop
They should get: [ ok ] Stopping wdmcserver: wdmcserver.
Edit to add: Further the following thread show the same system response as being normal.
https://community.wd.com/t/how-to-stop-from-constantly-building-thumbnail-previews/92195
