Trying to start playtest gives error message

Here's the error message I'm getting:
TypeError
this._scene.attachreservation is not a function

It happens whenever I try to playtest my game. Does anyone know what could be causing this? I haven't changed any plugins and the only thing I really did was create some really huge common events, maybe it just can't handle those? I'm talking massive, by the way. It's an entire crafting system in two common events with over 1,000 different combinations. The editor lags when I open them. That's really the only thing I've changed since I've been able to open the game, though. It could have been a recent update but I don't recall if I had changed anything before or after it. I'm going to start going through my plugins and turning them off one by one to see if I can find the culprit but in the meantime if anyone happens to know where I should be looking right off the bat that would be super.

EDIT: I also added all of my enemies/troops to the database before I did the crafting system. Never tried to playtest it while making the enemies and crafting but now I need to :p

Just tried turning on and off my plugins, nothing changed.

I took all of the js files from the NewData folder and replaced them with the ones in my game. I now no longer get this error, but instead it broke the TDDP Preloader. It can't find my files and returns an error that asks if they exist or not. If I turn the preloader off, I get an error saying "Uncaught Syntax Error: Unexpected token c in JSON at position 118075." Is it possible to revert to a previous version of MV? My game must just not like playing with new files (it was originally created on the first version of MV and was presumably fine up until the latest update). Replacing the preloader with the version found in DLC folder of the Steam commons folder for RPG Maker MV and leaving it on also returns the same Syntax Error.

I assume that this is now more of a JS issue than it is an engine issue, if you need to move my thread there I apologise.

Another EDIT: Seems like my game had the js files as 1.5.0, a version that is not available anymore :l

EDIT: Solution found!
After updating all of my JS files to 1.6.1 and all that good stuff, the issue became Iavra's Localization plugin. I'm going to go looking for an updated version of it and hope and pray to the good heavens above that there is one because all of the text in my game is in a .txt and porting it all back over to the engine would be a pain in the ass xD