Steam Cloud Unavailable?

I'm going to necro this thread rather than create a new one:

Did you resolve your issue? This started yesterday for me and still isn't working today. I can't upload a single screenshot.
It's not an issue with my installation of Steam because I tried uploading from another computer and it gave me the same error. Yet my friend was able to upload a screenshot on that computer from his account. So the issue seems to be with my account but Steam says I have plenty of available storage left in the cloud.

EDIT: The issue disappeared a few days later. Phew. I was not looking forward to contacting Steam support.