OK, same effect here. Here's a PDF, DOC, and XLS file. All appeared to transfer successfully, and all had an error when they arrived. The original files were all verified to work properly, and still do.
FTP is clearly broken on the DNS-323!
Microsoft Windows [Version 6.1.7600]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.
C:\Users\xxx>ftp dlink
Connected to dlink.
220---------- Welcome to Pure-FTPd [TLS] ----------
220-You are user number 1 of 3 allowed.
220-Local time is now 10:25. Server port: 21.
220-This server supports FXP transfers
220 You will be disconnected after 5 minutes of inactivity.
User (dlink:(none)): testuser1
331 User testuser1 OK. Password required
Password:
230 OK. Current restricted directory is /
ftp> dir
200 PORT command successful
150 Connecting to port 61372
-rwxrwxrwx 1 testuser1 702 24576 Mar 19 2009 test1.doc
-rwxrwxrwx 1 testuser1 702 38400 Oct 18 11:13 test2.xls
-rwxrwxrwx 1 testuser1 702 288161 Sep 29 14:50 test3.pdf
226-Options: -l
226 11 matches total
ftp: 814 bytes received in 0.00Seconds 407.00Kbytes/sec.
ftp> get test1.doc
200 PORT command successful
150-Connecting to port 61384
150 24.0 kbytes to download
226-File successfully transferred
226 0.002 seconds (measured here), 10.60 Mbytes per second
ftp: 24602 bytes received in 0.00Seconds 24602000.00Kbytes/sec.
ftp> get test2.xls
200 PORT command successful
150-Connecting to port 61389
150 37.5 kbytes to download
226-File successfully transferred
226 0.003 seconds (measured here), 13.17 Mbytes per second
ftp: 38944 bytes received in 0.00Seconds 38944.00Kbytes/sec.
ftp> get test3.pdf
200 PORT command successful
150-Connecting to port 61394
150 281.4 kbytes to download
226-File successfully transferred
226 0.018 seconds (measured here), 15.11 Mbytes per second
ftp: 290183 bytes received in 0.01Seconds 20727.36Kbytes/sec.
ftp>