What could be the cause of the following exception that occurs while trying to list the directories?
Caused by: com.enterprisedt.net.ftp.FTPException: 4
at com.enterprisedt.net.j2ssh.sftp.SftpSubsystemClient.a(SftpSubsystemClient.java:1109)
at com.enterprisedt.net.j2ssh.sftp.SftpSubsystemClient.openDirectory(SftpSubsystemClient.java:496)
at com.enterprisedt.net.j2ssh.SftpClient.ls(SftpClient.java:574)
at com.enterprisedt.net.ftp.ssh.SSHFTPClient.b(SSHFTPClient.java:1417)
at com.enterprisedt.net.ftp.ssh.SSHFTPClient.dirDetails(SSHFTPClient.java:1319)