Problems sending files through iChat to other mac users

Hey guys. I'm still a newbie at this. When i try to send or receive a file through iChat from other mac users it will not work. It works fine when i send it to anyone else but i've tried to send to three people with macs and it will not work. they seem to have the same problem. There is no firewall up. Does anyone know what the problem is?
Thanks

bump bump

No One??

http://docs.info.apple.com/article.html?artnum=107476


may help?

Thanks.. but the firewall isn't active..

hmm ill keep searching

well you can try posting something on here about it and maybe one of the apple tech people will know whats up with it.