MSN Messenger not sending files

[shybearuk]

I posted this question a while ago for my old system, but have now upgraded and am still having the same problem. My flat has a network of three machine. A cable connection runs to a machine running Windows ME via a Surfboard modem This machine in turn is connected to a network hub, and then routed onto my Ma's machine, running Windows XP Professional, and my machine running Windows XP home. Now the problem. When I am using Messenger I have no problem receiving files that people send to me, but am unable to send files to other people, resulting in an error message: 'The connection is blocked. please contact your system administrator'. Only thing is, I AM the system administrator. I've been told that it could be a firewall causing it, in which case how do I remove it from the central machine? I never personally installed one, so it must be something built into Windows ME. Oh yes, and if it makes any difference, the network was set up using a disk made on the XP Pro machine. Any help would be much appreciated.

[shybearuk]

Oops, one more thing. I CAN send/receive files to/from my Ma's machine via Messenger, so it's not a problem with my machine or hers, which is why I reckon it must be something to do with the Win ME machine.

[lisaj]

When you send a file through messenger, the sending machine opens a port for the receiving machine to 'pull' the file from. This port is hidden from the receiving machine because it is not directly connected to the Internet. Without mapping ports through your gateway machine to the other clients specifically for this purpose you'll find it difficult, if not impossible, to get it working. On the ME machine, are you using any firewalling software, or just Internet Connection Sharing?

[lisaj]

Sorry quick clarification having read that back to myself: The port cannot be accessed because the sending machine is not directly connected to the Internet.

[shybearuk]

I'm not using any firewall software to the best of my knowledge. I certainly haven't installed any, but yes to ICS. Now I'm going to possibly confuse the issue some more, when the ME machine was the machine that I used, it was still the gateway machine, but I couldn't send files from that either, and then it WAS directly connected to the 'net. So tell me more about this mapping ports thing. If it's not ridiculously tricky, I'll give it a go. I'm fairly good with machines (I'm an I.T. trainer) so I'm not too worried about making any major b*lls-ups.