I have the same problem when trying to upload an image from my own files. This message appears every time: Unable to create directory wp-content/uploads/2009/12. Is its parent directory writable by the server?
I read your suggestions and tried everything to no avail.
I have changed the miscellaneous settings into every possible configuration:
wp-content/uploads
wp-content/uploads/
/wp-content/uploads
/wp-content/uploads/
I have unchecked the organize by month box as suggested.
I have filled in the Full URL path to files.
I talked to the hosting company and was told that the permissions are set correctly.
Any other suggestions?