IE Plugin performance problem

[#1]

I'm trying to configure a Qlikview Server (9 RC5 x64) to be accessible from Internet (WAN). Everything works fine when running inside LAN. However, when accessed from outside the local network I got a performance problem with IE Plugin. A macro that change some variable values and set 20 inputfields contents runs in about 1 minute. That problem doesn't happen on AJAX client, on which the same macro takes about 1 second to finish.
Is there any reason for that happens? Am I missing some configuration?

System:
Windows Server 2003 x64
QlikView Server 9 RC5 x64
open ports: 80, 4747

Thanks.

[#2]

Check if port 4747 is really reachable, in and out from your and client networks, hope help.