FTP through ISA 2004 works for me, through ISA 2006 does not.....

In the process of migrating from ISA 2004 Enterprise Edition, 2 Servers in an array, to ISA 2006 Enterprise Edition, also 2 servers in an array, because the hardware is out of warranty.  2004 and 2006 ISA installs are on seperate hardware.
I have a Server publishing rule on the 2004 array for access to an internal FTP server, and can access it just fine from an external link. Internal FTP server is configured to allow only particular IP addresses to connect as anonymous.  FTP Server is IIS on Win2K3 R2 SP2 Enterprise Edition. Default gateway is set to the internal IP of the 2004 ISA array.  Have also tried changing this to the internal IP of the 2006 ISA array without getting a successful connection.
Server Publishing Rule on BOTH arrays is as follows on the appropiate tabs: Allow--FTP Server--Anywhere--IP OF INTERNAL FTP SERVER (Requests appear to come from original client)--External--Always.
The rule on the 2004 array gets me through straight away to the FTP site and I can see the traffic on the logging tab.  The SAME rule on the 2006 array gets me no where, with a Action & Result Code on the logging tab of "Failed Connection Attempt" 0x8007274c WSAETIMEDOUT respectively.  On the client I get an result of "The FTP session was terminated"
If I change the rule on the 2006 ISA array to "Requests appear to come from the ISA server computer" and then try to conenct from same external IP, I get the authentication box for an FTP site on the client (unexpected as it should be connecting as anonymous, yes I have tried this also), and on the ISA log I can see the connection attempt Initiated and then closed instantly.  If I enter in a Username and Password that I know has permissions on the folder that the FTP site is pointed to in IIS, same thing, connection initiated and closed instantly.
Why does the same rule not work in 2006 as it does in 2004?????
Buggered if I can get my head around it, all help much appreciated.
Cheers