I just downloaded it a few hours ago, and no, it doesn't work.
This is what YOUR server.cs says:
exec("Add-Ons/System_ReturnToBlockland/RTBR_ServerControl_Hook.cs");
What it SHOULD say:
exec("Add-Ons/System_ReturnToBlockland/hooks/serverControl.cs");
You obviously didn't read what "RTBR_ServerControl_Hook.cs" says.
It still exists, but doesn't work anymore.
You have to use the "serverControl.cs" in the "hooks" folder.