Just tried the Set Association command, and a few manipulations to see what happens. It didn't solve my issue still, but at least I progressed a bit in the assimilation of the system.
When I create the group association in LinuxMCE, and after I check it in the Seluxit software, it's well updated, but only the dongle appears in the group, the switch doesn't belong to any group. I tried also to set the group directly in the Seluxit software, both devices belong to the same group, but back to lmce, I don't have positive results so far.
I was just wondering, is it possible to associate lights directly in lmce without having to use the Seluxit software? I still couldn't find how to do it (after few trials, unfortunately the lack of documentation for the devices I'm handling is very problematic). If yes, I would try to configure everything from lmce.
Thanks for your support Hari, I hope it will get solved somehow