Can't Upload Photos- "Failed to write file to disk".

I cannot upload photos to my blog due to “Failed to write file to disk”. I updated to the latest version of WP and contacted my host who confirmed it was not a space issue. My host also uses a “cloud” server, which means I am not just on one server, so it can’t really be a problem with the server either. Is this a WordPress issue? How can I fix it? Is anyone else experiencing this problem? I’ve tried uploading a bunch of different photos, even ones I’ve uploaded before and none of them will upload. PLEASE HELP!!