IIS works on all ports on local LAN, only some ports remotely

Can anyone help me? I can't access any IIS websites on my Windows 2003/SP2
server from outside our LAN, except if it runs on port 80. What could cause
this problem, which appears to be a server problem (rather than a firewall
problem)?

I want to run a HTTPS server at a nonstandard port, say
https://myserver.mylan.com:9999/. I can access it from compute inside the
local lan (where the address gets mapped to 10.2.xx.xx), but from a remote
computer (which maps it to some number like (207.xx.xx.xx) outside the LAN,
I can not access it. Meanwhile, HTTP on the standard port 80 works fine.
In fact, if I change my standard http web site to listen to port 9999, I
have the same problem: http://myserver.mylan.com:9999/ works only from
inside, not outside.

The IT folks opened up the firewall for this port 9999. Also, this used to
work, I installed some updates since then (I think I installed SP2), and now
I can't get to this port anymore.

Does anyone have any suggestions as where to start looking?

 

Yeah, they confirmed that nothing changed. The port was working until I
installed a few updates (a few updates, a few apps, added memory, and added
a new HD).

How about this... If I wanted to block access to certain ports from
computers that are not on my local lan, how would i go about doing this?