Everything worked fine for about a week, but now my phone sync is failing. I checked the permissions on the "write" directory and am logged in as an administrator on this PC. I also even tried running the Windows Phone app for desktop "as administrator" but it crashes when it tries to hook into my iTunes library.
The phone is a Lumia 1020 and the PC is Windows 8. There is plenty of drive space and I can interact with that folder manually using Explorer with no permission issues.
Here's a screenshot.
It went away on its own, but I had done some major cleaning, permission repair, and even a firmware update on my phone since.