I downloaded the test project from KC Mirrors and tested it there. I got the same crash. Then I fixed and the crash no longer happened. I will update the plugin again, maybe I made a mistake. otherwise, you have to either guide me to reproduce the error or send me a project so I can test it.
(EDIT) Also, My Char Manager plugin was below the KC Mirrors on my tests. Eli Book is the same version.
I didn't understand the last question. When using the filename common event, the plugin commands arguments that are related to finding a character by its ID, when you set 0, it will be referencing the character that is changing its filename. That is the expected behavior at least ^^''
This is not working for you?