I have a worpdess multi site installation.
Yesterday, I upgraded to WP version 3.5 and upgraded all the sites in the network.
Today I created a new sub-site and I get the following error message on every page of the dashboard for this new sub-site:
"Upload folder is not writable. Export and file upload features will not be functional."
I don't have this message on the old sub-sites, just on this new one.