underlying connection was closed: An unexpected error occurred on a receive. at System.Net.WebClient.UploadFile(Uri address, String method, String fileName)

I upload a zip folder to different ftp servers using the following code.
Using WC As New WebClient WC.Credentials = mycredentials WC.UploadFile(target, fileName) End Using
One of the ftp servers gives me the following error (even though the complete zip folder was uploaded):
<div></div> underlying connection was closed: An unexpected error occurred on a receive.
   at System.Net.WebClient.UploadFile(Uri address, String method, String fileName)

The only difference between this and the other ftpServers is,  - soon after the folder is uploaded, it is removed by the ftp server.
Why do I get this error and what to do about it?