I recently noticed that Empty Mail filter wasn't in the list of my filters even though I thought had installed it. So I installed it again and it still didn't show up. On looking around I found that it had installed in the Program Files(X86)\Spamhiliator\Plugins folder when the main programme is in Program Files\Spamhililator and at the same time noticed a number of other plugins were also in the same state.
It appears that the installer for the plugins doesn't recognise where the main application is installed.
To overcome the problem copy any plugin which installs in the X86 folder to the Plugins directory for the main application - but not the Plugins3 directory.