-In a detailed log.dat one can see the following error:
FTP   I TRACE     Prot trace for: FTP-CI-OCEPER   (8168  ) req:Write len:4      Prot:FTP <- S FTP-CI-OCEPER 8168
FTP   I TRACE       0000  50415356                            [PASV]
FTP   I TRACE     Prot trace for: FTP-CI-OCEPER   (8168  ) req:Read  len:49     Prot:FTP <- R FTP-CI-OCEPER 8168
FTP   I TRACE       0000  32323720 456e7465 72696e67 20506173 [227 Entering Pas].
FTP   I TRACE       0010  73697665 204d6f64 65202831 302c3133 [sive Mode (10,13].
FTP   I TRACE       0020  332c3134 2c32382c 3233342c 31333429 [3,14,28,234,134)].
FTP   I TRACE     Prot trace for: FTP-CI-OCEPER   (8168  ) req:Write len:38     Prot:FTP <- S FTP-CI-OCEPER 8168
FTP   I TRACE       0000  53544f52 20464444 5f303439 325f3230 [STOR FDD_0492_20]
[..]
FTP   E CMD_ERR   FTP-CI-OCEPER(8168) [22365] STOR : 425 Can't open data connection.

-What is the cause for this error?
-How to solve the "Can't open data connection" error?

* To solve this error one of the following solutions should be applied:
1. Use Active FTP
or
2. Establish a port range with the partner and open these ports on the firewall.