Gets bounced off connection after "CLNT FileZilla"

Trying to use winSCP for a ftp connection to a webhosting service always results in disconnect (from debug log):

. 2008-07-25 11:36:05.214 --------------------------------------------------------------------------
. 2008-07-25 11:36:05.214 WinSCP Version 4.1.5 (Build 410) (OS 5.2.3790 Service Pack 2)
. 2008-07-25 11:36:05.214 Login time: 25. juli 2008 11:36:05
. 2008-07-25 11:36:05.214 --------------------------------------------------------------------------
. 2008-07-25 11:36:05.214 Session name: webservicehost
. 2008-07-25 11:36:05.214 Host name: webservicehost-name-modified (Port: 21)
. 2008-07-25 11:36:05.214 User name: our-username-modified (Password: Yes, Key file: No)
. 2008-07-25 11:36:05.214 Tunnel: No
. 2008-07-25 11:36:05.214 Transfer Protocol: FTP
. 2008-07-25 11:36:05.214 Ping type: -, Ping interval: 30 sec; Timeout: 30 sec
. 2008-07-25 11:36:05.214 Proxy: none
. 2008-07-25 11:36:05.214 FTP: Passive: Yes
. 2008-07-25 11:36:05.214 Local directory: default, Remote directory: home, Update: No, Cache: Yes
. 2008-07-25 11:36:05.214 Cache directory changes: Yes, Permanent: Yes
. 2008-07-25 11:36:05.214 DST mode: 1
. 2008-07-25 11:36:05.214 --------------------------------------------------------------------------
. 2008-07-25 11:36:05.308 Connecting to our-webservice-host-modified ...
. 2008-07-25 11:36:05.308 Connected with our-webservice-host-modified. Waiting for welcome message...
< 2008-07-25 11:36:06.401 220 Gene6 FTP Server v3.8.0 (Build 34) ready...
> 2008-07-25 11:36:06.401 USER our-username-modified
< 2008-07-25 11:36:06.448 331 Password required for our-username-modified.
> 2008-07-25 11:36:06.464 PASS ********
< 2008-07-25 11:36:13.135 230-Disk Quota - Current : 11.286 MBytes - Max : 500 MBytes - Available : 488.714 MBytes
< 2008-07-25 11:36:13.135 230 User our-username-modified logged in.
> 2008-07-25 11:36:13.135 SYST
< 2008-07-25 11:36:13.198 215 UNIX Type: L8
> 2008-07-25 11:36:13.198 FEAT
< 2008-07-25 11:36:13.229 211-Extensions supported:
< 2008-07-25 11:36:13.229 AUTH TLS
< 2008-07-25 11:36:13.229 CCC
< 2008-07-25 11:36:13.229 CLNT
< 2008-07-25 11:36:13.229 CPSV
< 2008-07-25 11:36:13.229 EPRT
< 2008-07-25 11:36:13.229 EPSV
< 2008-07-25 11:36:13.229 MDTM
< 2008-07-25 11:36:13.229 MFCT
< 2008-07-25 11:36:13.229 MFMT
< 2008-07-25 11:36:13.229 MLST type*;size*;create;modify*;
< 2008-07-25 11:36:13.229 MODE Z
< 2008-07-25 11:36:13.229 PASV
< 2008-07-25 11:36:13.229 PBSZ
< 2008-07-25 11:36:13.229 PROT
< 2008-07-25 11:36:13.229 REST STREAM
< 2008-07-25 11:36:13.229 SIZE
< 2008-07-25 11:36:13.229 SSCN
< 2008-07-25 11:36:13.229 TVFS
< 2008-07-25 11:36:13.229 UTF8
< 2008-07-25 11:36:13.229 XCRC "filename" SP EP
< 2008-07-25 11:36:13.229 XMD5 "filename" SP EP
< 2008-07-25 11:36:13.229 XSHA1 "filename" SP EP
< 2008-07-25 11:36:13.229 211 End.
> 2008-07-25 11:36:13.229 CLNT FileZilla
. 2008-07-25 11:36:13.229 Disconnected from server
. 2008-07-25 11:36:13.229 Connection failed.
* 2008-07-25 11:36:13.229 (ESshFatal) Connection failed.
* 2008-07-25 11:36:13.229 Disconnected from server
* 2008-07-25 11:36:13.229 Connection failed.
* 2008-07-25 11:36:13.229 AUTH TLS
* 2008-07-25 11:36:13.229 CCC
* 2008-07-25 11:36:13.229 CLNT
* 2008-07-25 11:36:13.229 CPSV
* 2008-07-25 11:36:13.229 EPRT
* 2008-07-25 11:36:13.229 EPSV
* 2008-07-25 11:36:13.229 MDTM
* 2008-07-25 11:36:13.229 MFCT
* 2008-07-25 11:36:13.229 MFMT
* 2008-07-25 11:36:13.229 MLST type*;size*;create;modify*;
* 2008-07-25 11:36:13.229 MODE Z
* 2008-07-25 11:36:13.229 PASV
* 2008-07-25 11:36:13.229 PBSZ
* 2008-07-25 11:36:13.229 PROT
* 2008-07-25 11:36:13.229 REST STREAM
* 2008-07-25 11:36:13.229 SIZE
* 2008-07-25 11:36:13.229 SSCN
* 2008-07-25 11:36:13.229 TVFS
* 2008-07-25 11:36:13.229 UTF8
* 2008-07-25 11:36:13.229 XCRC "filename" SP EP
* 2008-07-25 11:36:13.229 XMD5 "filename" SP EP
* 2008-07-25 11:36:13.229 XSHA1 "filename" SP EP

I have tried logging in with command line ftp which works fine.

Any ideas/suggestions ?

Do you see any reason for disconnection in the server's log? Note that your server announces support for "CLNT" command.

I do unfortunately not have access to the server / serverlog (it is commercially run by a regular webhosting company)

Best regards
Jesper K. Pedersen

OK, so then you should ask their support.