FTP, ICF and alg.exe

Hello

I have been having a problem with alg.exe crashing at windows startup.
The process reported a crash, but still ran and the internet
connection firewall (ICF) was still active.

I did find though that after a random period (not directly after the
crash message) I was unable to connect to any FTP sites. Now, the FTP
protocol works by the client (me) sending data to the server on port
21 and then the server making a connection back to me on some port
(determined by the server) to send the files. ICF deals with this by
somehow allowing the server to connect back to me on that port.

My problem was that I was somehow not even reaching the server! The
packets would never make it and I would get a connection refused.
Looking at the server logs (on a remote machine that I control) showed
that my client had never reached the server.

Now, I can stop alg.exe from crashing by removing the following key.

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ALG\ISV\{6E5 90D61-F6BC-4dad-AC21-7DC40D304059}]
"Publisher"="Microsoft Corp"
"Product"="FTP Client/Server Protocol"
"Version"="1.0"
"Protocol"=dword:00000001
"Ports"="21"

Now, after removing that key, I can connect to FTP sites, but cant get
a directory listing since ICF stops the server connecting back to me.
I therefore conclude that this registry key is doing the magic that
lets the ftp server connect back to my firewalled client and that this
same key is somehow causing alg.exe to crash.

All I need is someone to explain to me why all of the above happens.


Thanks for any information

Jonathan

P.S. I can solve these problems by using passive mode FTP after
removing the key - but that only helps me if the server I am
connecting to supports passive mode and does not help my understanding
of the problem. I have all the lastest updates etc for my system which
is a windows server 2003 box.