Download with 10 Threads Chrashes

i tryed to Backup a FTP Server so my Internet Conection is a 30MBit Cabel.
When i try do download and set the Number of Simult. Threads to 10 my SmartFTP Client is Crashing with.

Fehlgeschlagene Anwendung smartftp.exe, Version 4.0.1097.0, fehlgeschlagenes Modul smartftp.exe, Version 4.0.1097.0, Fehleradresse 0x00693a20.

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How i can fix this Problem?
greetings from Germany

Please provide instructions on how to reproduce it. For example with a publich FTP server.