I've moved this thread to Javascript/Plug-in Support. Please be sure to post your threads in the correct forum next time. Thank you.
The only way to get that kind of error is to add a plug-in or do major plug-in edits after you saved a game. Plug-ins *require* you to start a new game 99.99% of the time. If you do not get the error when you start a new game, then that was the cause, and you will have to do that if you wish to use that plug-in.