0 KB files received during FTPS transfers in Serv-U

8/5/2026 5:51 PM

8/5/2026 5:51 PM

0 KB XML files may be received in both the MTM and Direct EDI, and Wholesale folders. This behavior indicates that the file transfer may be starting but not completing successfully. Although folder permissions should still be verified, the issue is not necessarily due to permissions, as the same accounts can successfully upload files at other times.

 

Serv-U Managed File Transfer & Serv-U FTP Server

Based on the transfer errors reviewed, the following conditions may contribute to 0 KB files during FTPS transfers.

550 No such file or directory

This indicates that the server cannot find the file or folder referenced by the client.

Possible causes include:

• The client is using a path that does not exist on the server.

• The file was moved or deleted before the transfer completed.

• The directory name contains a spelling, case, or path mismatch.

426 Data connection unexpectedly closed

This error occurs when the FTPS data connection closes unexpectedly during the transfer. It commonly indicates a network, firewall, NAT, routing, or security-software issue.

Possible causes include:

• The firewall is blocking the passive FTPS port range.

• A NAT or routing device is closing the connection prematurely.

• Security software is terminating the encrypted data channel.

• The FTPS passive-mode configuration is not compatible with the network path.

FTPS uses a separate encrypted data connection in addition to the control connection. If the data channel cannot remain open, the transfer may stop before any file content is written, leaving a 0 KB file on the server.

550 Permission denied

This indicates that the connecting account was denied access to the requested operation. The account may not have the required write, overwrite, or delete permission for the target folder.

Possible causes include:

• FTP-server permissions do not allow the requested operation.

• NTFS permissions are preventing access.

• The file is locked or being used by another process.

• The client is attempting to overwrite or delete a file that it cannot modify.

If permissions have already been confirmed and the account can successfully transfer other files, this message should be correlated with the exact timestamp and filename before treating it as the root cause.

Transfer aborted with 0 bytes received

This message is consistent with a data-channel failure. When the data connection closes before payload data is received, the destination may create the filename but retain a file size of 0 KB.

Recommended next steps

1. Test the same transfer using SFTP on port 22 instead of FTPS on port 21.

2. Confirm whether the 0 KB files continue to occur during the SFTP test.

3. If the issue does not occur over SFTP, investigate the FTPS passive-port range, firewall rules, NAT or routing devices, and security software between the client and server.

4. Review the client and server logs for the exact timestamp and filename of a failed transfer. Focus on the related 550, 426, and connection-abort messages rather than collecting the full log if the file exceeds the attachment limit.

5. Verify that the client is using the correct remote path and that the file is not being moved, deleted, or locked while the transfer is in progress.

6. Confirm that the affected accounts have write, overwrite, and delete permissions in the target folders.

7. Resend a failed order and compare the successful and failed transfer logs to identify differences in the connection, passive ports, path, or transfer sequence.

The SFTP test is the recommended isolation step because it helps determine whether the issue is specific to FTPS passive-mode data connections. If the problem persists over SFTP, continue investigating the client application, file-generation process, remote path, file locking, and network stability.