Hi there!
I don't know what are you doing. I need to see what are you doing in order to help you.
1) First go to the main page of the plugin and download it from there.
2) Check if you are using EliMZ_Book somewhere above all other Eli Plugins
3) Are you using RPG Maker MZ right?
4) Show to me a screenshot of your plugin parameters, the character image that you are using for diagonal and the filename of that character image.
5) Are you using any other plugins that messes with diagonal or movement at all? If yes, send to me a screenshot of your plugin manager
6) When the game opens, press F8 or F12. A browser window will open. Go to the CONSOLE tab. Send me a screenshot of what is in there.