This is a common error that occurs in WordPress when trying to upload themes, plugins and images. If you install WordPress via Fantastico or a one click install script permissions are usually set correctly via that process.
However, if you install WordPress manually via FTP sometimes permissions are not set correctly.
And thus “directories” are not always writable.
In order to fix this problem;
- Login via FTP
- Click to wp-content directory
- Change permissions on /uploads and sub folders to 777
- Return to site and attempt original upload
- If works return to FTP and change permissions back to 755