My bad! Message Manager is indeed on version 1.1.0!
As I can see, you have a problem with the plugin parameters of the message manager. You need to check it and see if everything is properly filled. By the error trace, I guess the parameter causing the error is one of those:
They need to be filled because they will decide the window message and window name box position.
Since the error is happening, the RPG Maker is not recognizing that the plugin is ON, and therefore, the message scroll will also not work properly.