2.0.7. can’t upload files

After having updated to 2.0.7 release (from 1.5) I can’t upload files anymore in one of my blogs.
I get the message:
“Failed to write file to disk”
I changed the permissions on wp-content folder (including the uploads folder inside it) to 777.

Also, the problem is in a blog placed in subdomain:
https://blog.example.com
and not in the blog:
https://example.com/blog
(obviously same releases and same features)

Has anybody any ideas on what’s happen?

Thanks