Unity Fatal Error: sharedassets0.assets.resS:

I've been getting the following fatal error on Unity 5.5.0 that prevents me from being able to launch my project. This started happening after a material import froze and I had to manually end the process and close Unity:



The blacked out part is my project name (root project folder, not a build folder), so it's looking for this resources file in the root project folder. I checked a backup that I have of this project from 3 days ago and also much older projects unrelated to this one, and I do not have this file in the location it's looking for here in any of those. Why is it looking for this file in the root project folder when the only place it usually shows up is the build folder?

Can someone please help? Thanks in advance.