I have been reading about a similar problem here, but none of the posts has helped, so I hope this one does :)
When trying to upload a file attached to a post (for the first time) I get an error message saying that the folder .../uploads/2007/11 could not be created.
When I look at the uploads folder, I see that the 2007 folder has been created by WP, but there is no "month" folder underneath. When I create the month folder manually with all permissions (777) the upload still fails with exactly the same message...
Other than making sure that permissions are right, I have also tried changing the WP configuration to use a different uploads folder every time - no good.
Any possible solution to this will be greatly appreciated. I find it weird that WP is able to create one folder, but then below that the sub folder (and eventually the file) cannot be saved.