Client closed the connection??

I,m trying to upload a large set of folders and subfolders. What to do with the following problem that occurs after minutes or seconds from starting the upload.

i have changed the keep alive mode interval to 960 s and added NOOP and LIST to the commandline (i don't really understand why, i read the tip somewhere.)

the following occurs:

LIST -aL
150 Opening ASCII mode data connection for file list
117 bytes transferred. (680 bytes/s) (172 ms)
226 Transfer complete.
Remote file exist check: 'README'.
SIZE README
550 README: No such file or directory
PASV
227 Entering Passive Mode (69,50,210,183,166,52).
Opening data connection to 69.50.210.183 Port: 42548
STOR README
Timeout (20s).
Active Help: https://www.smartftp.com/support/kb/45
Client closed the connection.
Transfer failed.

Try using active instead of passive mode.

Can you give me a clou where to change this mode?

Thanks anyway for your quick respons,

Teus

Look on the toolbar.
It is the 9th icon from the left. It is labeled "PASV"