Hey there.
While the problem you encountered was definitely an issue that didn't happen without my plugin, the reason it caused an error in the first place was because of the misconfiguration of EquipCore, not because of something wrong with Dual Wield. There is a note in the documentation (or I think there is anyway) that advises to make sure you've actually given the actor the dual wield equip type, and not just given them two weapon slots via equip core, otherwise you'd have problems.
By taking away all of their weapon slots, the bit of code that swaps weapons around gets confused and doesn't know what it's doing anymore, causing the crash. Technically that could be considered an issue with my plugin, but the default state would be to always have at least one weapon slot , so it'd usually be safe to assume that the actor has at least one.
Also, it looks like the version of the menu extension you're using is a little bit older, as the line it references in the crash does not match with that function in the latest version. I'm not saying you should update it, but the latest version does fix a display issue with YEP_ExtraParamControl which you are using.
~Ramza