This is the first time I have come across this problem. This will probably have something to do with the languages things I have put it. I have updated this slightly for the next release though I don't think it will help this problem very much. Would it be possible if you could send a copy of the debugger to my email address ( mark [dot] kernke [at] gmail [dot] com ). To bring up the debugger you will need to firstly go into the plus preferences > General > Scripts > check the box "Enable debugging options (for script developers only". This will bring up a new window and it is the log in there for Message Customizer! Live that I would like (you might need to restart the script or messenger to get me all the information I would like (and then make sure you sign in and try the menus). That information should be enough for me to understand what happened.
One thought of mine for the reasoning behind this is because your friend might not have selected a language option on the first start-up and there will be a problem whenever it tries to get information about the selected language. To fix this you must first uninstall the script and then re-install it and select a language when prompted and press ok to it. Without this their will be problems in the current build, I will fix this up for th next release however (hopefully).
Thank you for reporting the problem
.