Ok, here's the situation: I've got iTunes installed on 3 of the PCs on my home network, and each computer is set to share music with (and play music from) all the others. With my parents' computers, this works fine, and my computer can play music from both of theirs. However, the trouble comes when I'm using one of their computers and want to play my own music on it. I can look at my library fine, but as soon as it comes to playing anything, it doesn't work - the entry comes up with a little (!) mark next to it, and refuses to play. Here's what I've tried doing to solve the problem: I've tweaked my firewall settings to allow all the ports that iTunes uses (with help from this guide). The firewall (Outpost) now does not log anything as being blocked, so I am assuming that it is getting through the firewall without any problems. I have also tried disabling my firewall completely, to no avail. I have tried creating a separate user profile, putting a couple of sample MP3s in its library, and playing from another computer. This didn't work, so it would seem to be a computer-wide problem. I have tried disabling all but one of my network cards (strictly speaking I have 3, if you count my Bluetooth adapter, which my computer does). I still don't seem to be able to play my music from another computer, and I don't know why. I had the same problem at Uni, so it would seem that it's not something specifically to do with my home configuration. Any thoughts?