Failed to Insert Item - Can't attach new sprite collections/animations to object

[Werezompire]

Not sure what's going on since this is affecting previous builds that were working fine. Anyway, say I've got a tk2DSprite script & tk2DSPriteAnimator script attached to an object. If I try to use the tk2DSprite Collection drop down box to change sprite collections or the tk2DSpriteAnimator Anim Lib drop down box to change animation libraries, I get hundreds of error messages "Failed to Insert Item. Name:" followed by the name of the sprite collector or anim library that I can't access and an incrementing command #. With the Sprite Collections, it's alphabetic (so everything after a certain point in the alphabet just doesn't show up) & with anim library is based on oldest to newest so any new anim library I create is inaccessible.

With Sprite Collections, I can get around not being able to use the drop down menu by drag & dropping it, but that doesn't seem to work on anim library. So I'm kind of sunk with not being able to use half my animations & ALL new animations. Game seems to run fine in its current state, but I can't really edit or add anything to it without being able to attach animation libraries. Not sure how to fix this.

I'm using Unity 5.6.6f2 & 2.5.8.9 on a Win10 laptop.