retrying when uploading

Hi all
When I upload files vie Smart FTP it keeps retrying for a lot of the files. When it's retrying a file, other workers won't keep uploading which means that it takes forever to upload large folders.
In another thread someone else who had the same problem was asked to post the log for one of the retried files, but that thread does not offer a sollution. Here is the log:
[08:10:51] Resolving host name ""
[08:10:51] Connecting to Port: 21
[08:10:51] Connected to
[08:10:51] 220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------
[08:10:51] 220-You are user number 9 of 100 allowed.
[08:10:51] 220-Local time is now 08:10. Server port: 21.
[08:10:51] 220-This is a private system - No anonymous login
[08:10:51] 220 You will be disconnected after 15 minutes of inactivity.
[08:10:51] USER
[08:10:52] 331 User OK. Password required
[08:10:52] PASS (hidden)
[08:10:52] 421 I can't accept more than 4 connections as the same user
[08:10:52] Active Help:

Just as an extra piece of info: I'm using only four workers.

Please help, thank you.

Hello ..

Your server has a 4 concurrent connection limit.

1. Menu: Window->Close ALl
2. Set the number of workers in the transfer queue to 1

Right. So I did what you recommended me. I stil get some retries.
[07:34:12] PORT 192,168,2,3,194,164
[07:34:13] 200 PORT command successful
[07:34:13] 500 ?
[07:34:13] STOR comment.php
[07:34:13] Transfer failed.

The next file smart ftp tries to upload then stalls while it says retry with the other file and the upload takes forever as before...

Your server does not let you upload. Please contact your web hosting provider / server administrator for assistance.