Sorry for the delay in replying. I can reliably and consistently reproduce this problem.
It is very simple. When the ScriptMaster 5.2/5.3 plug in is first enabled it attempts to start up and launches a java process which it then fails to connect to. When it is enabled a second and subsequent times it launches a new Java process as before but connects to the Java process launched previously. The plug in then operates correctly albeit with an additional unused Java process.
So it appears to start up correctly if there is a Java process still running from a previous attempt to enable the plugin.
To reliably reproduce the issue I quit any existing Java processes using activity monitor. The first attempt to enable the plug in will then fail. Subsequent attempts then succeed.
Basically the scriptmaster plug in 5.2/5.3 is not managing the Java processes and connections correctly.
The email plug in appears to work ok.
PS Having said that the email plugin may be picking up Java process launched previously too!