Hello,
Thanks for reporting this! After some brief testing it looks like our plugin is not currently compatible with YEP_X_ExtMesPack1, and very likely pack 2 as well. If you turn off that plugin, things should work properly. If not, please let me know and I'll try to figure out if there are several issues.
In the meantime, I'm adding compatibility with those message packs to my list of tasks, so look forward to that in a future update.
As an aside, I'm not sure why but YEP_X_CoreUpdatesOpt introduces a graphical bug where the images don't load right the first time you enter a battle/skill menu. It's not as bad as the crash you reported, but it's still not ideal. I'll look further into this one too.
-Isiah