FluentFTP file transfer

Hi, I’m using FluentFTP in a VB.Net project in which I create some .XLSX files to be transferred to a specific FTP address. The procedure is able to connect to the FTP and to transfer the file. The problem is that the transferred file has 0 bytes size (the created file is about 10 K).
if I try to transfer the file using Filezilla, all works correctly, so I think there is not a connection proble.
here is the code I use to transfer the file:

client.Host = ftpHost
client.Credentials = New NetworkCredential(ftpUser, ftpPassword)
client.ConnectTimeout = 600000
client.ReadTimeout = 60000
client.EncryptionMode = FtpEncryptionMode.Explicit
client.SslProtocols = System.Security.Authentication.SslProtocols.Tls12
client.DataConnectionType = FtpDataConnectionType.PASV
client.Connect()

client.UploadFile(fileexpDef, “/OUT/” & newFile, FtpRemoteExists.Overwrite, False, tpVerify.Retry)

If i run the program in debig mode, all the variables have the corect values.
Can you help me?
Thank you