Problem with filesharing over a WiFi LAN


I have a couple of computers set up on a WiFi LAN. The computer with CPF running is connected to the WiFi router via ethernet. The computer without CPF running is connected to the router via WiFi. I’m trying to share a directory on each computer but CPF appears to be preventing me: when it is turned on, I cannot connect to the remote directories on either end. However, if I turn CPF off, connect to the directory in question, then turn it back on again, I can browse, download, upload, etc. without problems until some time passes (not sure how long exactly, about 20 minutes), after which time I have to repeat the process. However, if I leave a shared directory open in windows explorer, it connects fine, even if the other computer can’t connect.

I’ve defined the network card that connects to the router as a trusted zone.
Svchost.exe does not appear in either the application monitor or the component monitor.
The logs have no messages appearing when I’m failing to connect.

I am running CPF on Windows XP with SP2.

Please help. No doubt it will be something asinine that I’m overlooking, but this is really doing my head in…