Update 4 (February 06):
Google has officially confirmed that the client’s latest version 3.39 has added support for network-attached storage (NAS) devices. Here’s how you sync photo/videos to Google Drive and Google Photos from NAS devices using Backup and Sync:
To start syncing, mount the network device to your Mac or PC. In the “My Computer” section of the Backup and Sync Preferences, click Choose Folder. Select the mounted folder or subfolder, and click Open. Click OK. Network folders sync periodically only while mounted on your computer
Update 3 (February 01):
Backup and Sync’s latest v3.39 is out. Try installing that and see if the client’s new version fixes the issue.
Update 2 (September 09):
Backup and Sync’s updated version (3.36) supports FAT, confirms Google.
Update 1:
We tried reproducing the issue at our end, and we can confirm that Backup and Sync app doesn’t feature the ability to sync stuff kept on network drives. The following screen shot shows the description of error D41D8CD9 that appeared in our case.
Original story here
An expert on the official Drive forum recently shared that in some cases, while setting up the Backup and Sync app during installation, Google Drive Error D41D8CD9 shows up. As the error does not describe what it is pertaining to, the expert further explains that it occurs when Drive is not able to sync folders (Desktop, Documents, or Pictures) that are enabled for sync and backup by default when the app is installed.
To get more clarity about the error, he suggests those facing the error should deselect and reselect the folders checked by default, something which they can do by heading to the application’s Preferences section**. As a result, Google Drive error notification will then display the actual cause stating “The folder documents can’t be synced. Please select a folder on an NTFS drive that is not mounted over a network”.
As per his observation, the error occurs when the folders being synced are not on local drive (meaning they are network-mounted). But as clear for the error message in the last paragraph, the notification will also show up in case of a local but non-NTFS drive.
Some quick googling revealed that the Mountain View, California-based company officially accepts this as a Backup and Sync limitation. Here’s what’s written on the Google Drive FAQ page:
The Drive sync client supports only HFS+ (on OS X) and NTFS (on Windows). There is currently no support for network volumes (e.g. SMB or NFS) or other file systems such as FAT32.
There are also some stray reports of users getting the aforementioned error while dealing with locally mounted folders on a Windows 7 machine (which is NTFS). We are not sure what’s the problem in that case, although it could well be a false alarm.
So the key takeaway from this discussion is that the new Backup and Sync is useless if you are only dealing with network mounted folders. Also, the NTFS-only condition may also upset some potential users. Since, the same client is used for Google Photos also, the issue should affect them as well (in fact, that seems to be the case).
**Note: A user highlighted in the official Drive forum that the Error D41D8CD9 occurs in a way that they can’t access the Preferences option, rendering them helpless.