suddenly... "Cache unable to write..." (Win10)

Hey all,
This issue is driving me nuts. I have been working in CI4 for quite some time. And everything has been working great. On refresh today out of the blue, my application started throwing: "Cache unable to write ...xxx.../writable/cache"

I'm in Windows 10. I tried checking permissions of the writable folders and everything has full control. The "read only" box is showing as checked for the folders but from what I understand that is not an issue for file permissions and I can't uncheck it anyway, so that's annoying but should be fine? 
I can't figure out why this would all of the sudden happen. I did just install the new Google Drive app right before I started getting the error, and maybe that did something global to file permissions? I tried doing a global check and repair on the filesystem and that didn't help. Just checked my other CI projects and they are all failing in the same way now. Any suggestions on how to repair cache that suddenly starts failing?

Cache unable to write to
Cache unable to write to