No connection ...again

Hi,
I'm getting the following error on all of my servers/domains:

No connection could be made because the target machine actively refused it. Connection closed.
No such host is known.
Connection timeout. No response from server.

It's more or less this (https://www.smartftp.com/support/kb/58) error message. I checked everything, the ftp connection details are 100% correct. I don't have any firewalls that block outgoing connections, WindowsXPsp2 firewall itself knows about SmartFTP (current version). Also, I don't use overrated, bloated Antivirus Software (just AntiVir personal edition), so that's not an issue, as well as Adaware is updated and runs regularily. Furthermore, my Trendnet router TW100-S4W1CA_E (http://www.trendware.com/asp/download_m ... YPE_ID=661#) is up to date as well... what else could be a reason? A server side setting by my provider perhaps? I tried out active and passive connections, but nothing helped, except restarting Windows. What's going on?
Any hints are appreciated!
ciao

Grendel