How to make network shares available using FileZilla Server
I recently ran into this issue as have a lot of others it seems. So you want to setup FileZilla Server to share a network resource instead of a local one. You've probably tried setting it up as a mapped network drive. You can transfer files to it all day long in Windows, but it just won't work as a shared FTP folder. You get the FTP 550 error. And so on and so you will for all eternity if you don't recognize a few key elements about how this process really works.
The directions below are not a step-by-step pictorial reference. It assumes you have at least a basic understanding of how to use Windows and computers in general.
Big Deal #1
Permissions. You need to set FileZilla Server to run as a different user. This is not the whole puzzle, however, so simply running FZS under your normal administrator account will not solve your problem. To accomplish this is easy enough. Go to your Control Panel and open Administrative Tools. Open Services and locate the FileZilla Server row. Open the properties page for it (double-click) and go to the Log On tab. Enter a local username and password here that you wish to use. I strongly suggest you make a new user account for this task. Make it an administrator to start with just so you know it works...do proper security later. You will need to restart the FileZilla Server service for this to take effect.
Big Deal #2
Mapped drives aren't good enough. You need to set up the remote folder as a network location. To do this, you have to go to My Network Places. You can get to that (in XP/Server2k3) by going to your Control Panel, opening Network Connections, and clicking on My Network Places in the bar to the left. It's the Other Places group--expand it if it is closed. Once you're there, again look to the left bar thing and click on Add a Network Place. Go through the wizard and provide the network URL for what you want to share where appropriate. Name it anything you feel like.
Big Deal #3
Share your new "Network Location" that you made. In FileZilla Server, when you add a folder for a user you can scroll past the local drives to the Network Locations node. Expand it and locate the network place you setup. Select it and use it like you were intending to use your mapped drive.
Big Deal #4
More permissions. It isn't good enough to just do the things above. You must also go to the computer you are sharing a resource from (the server your network resource is on) and create a user account with the same username and password as the one you made for FileZilla Server. You're still not done. You must grant that user account both sharing and file permissions on the folder you're trying to share across the network. Start with Full Control just so you know that you're working so far. Peel away permissions after you've successfully made your first test.
Ok, so why does this happen? Mapped drives aren't good enough because effectively they don't exist as far as a service is concerned (extreme oversimplification...I know). You also have to setup the user accounts so that both the file server and FTP server are "on the same page" as far as permissions are concerned. With file permissions explicitly defined and using network places (that do work) instead of mapped drives, your FTP server will be able to access the network resource as you expect.