File sharing with ZoneAlarm Pro

I have a desktop connected to a USB modem (broadband internet) which
then shares its connection wirelessly (Bluetooth) with my laptop.

The Internet Connection Sharing works well with ZoneAlarm Pro running
on both computers. (I set the relevant options). However despite both
computers being in the same workgroup, I am not able to access the
network drives on the computers whilst running ZoneAlarm.

To explain further: if I shut down ZoneAlarm on both computers I can
then connect to the C: drive on the desktop from the laptop, by
mapping it to a drive letter (usually I on the Laptop. However if
ZoneAlarm is running on either or both computers I am unable to do
this.

I have set the Bluetooth network (as automatically detected) to the
trusted zone in ZAP on both computers. On both computers, the trusted
zone security setting is Medium. I haven't altered any of the Custom
security settings - all are set to the defaults. There are no expert
rules or similar.

Have you any suggestions?

Thanks