I have a strange problem.
I have an FTP server setup at work, on a LAN using zFTPServer. The server is configured to listen on standard port 21, and accept passive connections through ports 40000 to 40100.
The server is behind a D-Link DI-704 Router. The router is set to forward ports 21, and 40000 to 40100 to the internal IP of the computer hosting the server.
zFTPServer has numerous users setup with all of their various permissions and mount points.
All computers, both internally on the LAN, and external to the LAN can logo on and do everything within the constraints of their user permissions. All computers accept ONE.
When I log on as a user that has Read/Write/Upload/Download privileges from my home computer, I can do everything accept upload. I can download, create folders, delete files/folders, but I cannot upload. For some reason on this computer, when attempting to upload, the upload hangs upon the FTP server attempting to open a data connection after entering passive mode. After 30 seconds or so, the upload fails completely with a 500 error (Access denied). This makes no sense as I am logged on as a user with more than enough privilieges (read/write/delete/append for files; list/make/delete/+subdirs for folders).
The host computer is running Windows XP Pro, with Symantec Antivirus Corporate 9.0...that's it. Aside from the Server software itself, no other uneccessary software is installed. Windows Firewall is DISABLED.
What could possibly be stopping this one particular computer from being able to add data to the FTP server (that is the only thing not working...i.e., if i upload a zero kilobyte file, it works..it is only when attempting to add physical bytes of data that this problem occurs)? It's almost as if the host computer is blocking my home IP address specifically from adding data, but I cannot find any evidence of this at the host computer itself. Could it be my specific Internet Connection from home (High Speed Cable)? I have no idea.
If anyone has any suspicions or suggestions, please let me know and it would be greatly appreciated.