When you setup an FTP server on a Windows Server 2003 system you may run into this issue if you are using RRAS and have configured the server as an Application Server (which causes the Application Layer Gateway service to start). There is a known issue with FTP and this configuration for downloading large files. However this can also affect an FTP server where "Allow anonymous connections" has been disabled.
To solve this you must configure the Application Layer Gateway (ALG) service to not make port mappings for your FTP server.
Here is the fix:
- On the server open Regedit
- Navigate to HKLM\Software\Microsoft\ALG\ISV
- Change the value of {6E590D61-F6BC-4dad-AC21-7DC40D304059} to Disable NOTE: not Disabled.
An IISReset is not required.
The Microsoft KB related to the large file download issue is here: http://support.microsoft.com/kb/931130/en-us