The TransferBytesXL property returns the number of bytes that
have been copied to or from the FTP server. This property
returns the number of bytes as a Double floating-point value
instead of a Long integer, making it suitable for very large
files that exceed 2 GiB in size.
If this property is read while a transfer is ongoing, the property
returns the number of bytes that have been copied up to that point. If
read after a transfer has completed, the total number of bytes copied
This property value is reset with every data transfer.