Trouble copying iTunes library across Buffalo WiFi network

I have set up a network with Macs and PCs in it

I successfully copied my itunes library from the PC to the Mac. It worked on
the Mac thereafter.

The PC's CD stopped working and then I started needing to put CDs on my iPod
so I put them on the Mac

Now I need to copy the library from the Mac to the PC. I have successfully
copied all the extra files to my MyMusic directory but when I came to copy
the recordings themselves, all I get is an error message telling me that
there isn't enough space available on the PC

So I tried copying only a part of the library onto the PC with the intention
of copying the rest in stages

But all I get is a few files copied and then an error message on the Mac
telling me that there isn't enough space on the PC. When I check windows
explorer, I find that there is nearly 4 gig of space on the PC. Anyone come
across this problem before?