You’re uploading images or plugins like usual and suddenly you get this error:
Failed to write file to disk.
I just did, and even though I Googled, there isn’t a fix offered that I could do on my own. The most recommended solution was to contact my web host and ask support to reset my files and folders permissions to default. Which I did. And voila! Back to normal. I can upload images and plugins again. I don’t know what caused the permission changes, I haven’t touched my site (except to publish posts) in weeks. Anyway, I’m just glad the fix was quick and pain-free.
I hope you solve your error as fast as I did mine *wink*