This is a WordPress error I received recently when migrating a site from a development domain to the live domain.
After checking the permissions on the folder \wp-content\uploads (if you don’t know how to do this, see here for an explanation), I did some digging and finally found that the problem was in Settings > Media in the ‘Store uploads in this folder’ box.
The folder for this site is /var/sites/m/mydomain.com/public_html/wp-content/uploads. This path is not the standard WordPress configuration, but it was for the host I was using at the time.
In this case, all you have to do is check that where it says ‘mydomain.com’ you replace it with your own domain, and then make sure that the letter preceding the site url is the starting letter of the site url.
So for this site, the path was /var/sites/j/jackdawwebdesign.co.uk/public_html/wp-content/uploads.
In my case, the url had been changed, but the letter preceding the url hadn’t.
It’s easy when you know how, isn’t it?