Hi,
I've been having this same problem (from the same tutorial), however I may be on to something. Make sure you check all your registry names to ensure that they are correct. For me the error message changed when I went back through and changed all my registry names to be the same thing.
Now I just get: "[Client thread/WARN] [minecraft/ScreenManager]: Failed to create screen for menu type: modid:registryname"
It's not a fix but at least it's no longer an error or even server side according to this.