Damit – that’s why they say: “Never change a running system!”. I had my WHS running with LightsOut (Green IT Software) and everything was working fine: the server woke up when a monitored client came alive and it went down when the last monitored client had gone… until a few weeks ago.
Honestly, I have invested more than just a few minutes to find out what has happened – the server was going down OK when the last client disconnected but failed to respond to the “wake-on-lan” packets when the clients tried to wake it up.
To make a long story short, I went the full nine yards, uninstalling LightsOut (WHS & Clients), reinstalling, updating, uninstalling again, etc. – to no avail. I then decided to check what I should have checked long ago: the settings of the network card on the WHS. Just to find out that the relevant NIC Settings did not enable WoL – for whatever reason… my best guess: some Windows Update might have delivered a new driver to the NIC or so – and settings had gone strange. After correcting them (to what the LightsOut manual lists as prerequisites) the WHS is now reliably responding to WoL calls again 🙂