Can't get to a apache server from outside with IE, can with FF & Chrome

[djago]

Hi

I'm using IPCop but I need more features that Zentyal can provide so I give it a shot.
I have a fixed IP connection and 30+ PC inside the company. a bunch of them are servers to the outside world for specific clientes serving with different ports (mostly Apache, but I have a couple of other servers). I'm forwarding ports with IPCop and it works nice.
BUT when I try to use Zentyal with same rules created I have a problem. I can't access to an apache with IE but I can with Chrome and Firefox.
There are no fancy configurations right now. Zentyal was installed on an old PC, then updated, and rules were created to allow external access.
Any clue?

Regards,
FSO