I just changed computers and installed ZoneAlarm Free I have an FTP server running which listens on port 526. My router is configured to pass incoming calls to the IP of my PC. When testing with one client for the first time on this PC, Zonealarm asked permission for the EFT server which I gave. The client could connect and everything seemed to work.

However after the client disconnected he could not reconnect anymore. Only after restarting of the server could the client connect again. To see what the problem might be, I did the following.

1) Client could connect one time, not the second time.
2) I disabled the firewall, now the client could connect. My conclusion is that Zonealarm blocks the incoming traffic. It shouldn't because it should know that the EFTP server is listening to that port.
3) I looked in the log and saw indeed that it had blocked that particular IP-address.
4) When I add the incoming IP to the incoming zone and enable the firewall, the client can access the server again.

Problem is that the client can login from any IP address, so the problem basically remains. Any idea why the first login to the server is accepted by ZoneAlarm, and the next attempts are blocked?

I also tested with version and had the same result. On my old PC I had a much older version and did not have this problem. I also tested with 3 different ports and with 3 different persons. All have the same problem that they can only connect once.