Unexpected error when configuring network bridge - not ICS related

I've just bought a new PC which I want to use as a media server,
connected via a crossover Ethernet cable to my Roku SoundBridge, and
via WLAN to my home gateway so I can access streaming Internet radio.

The PC has an 802.11g PCI card, and on-board Intel 10/100 Ethernet.
When I select both cards and click "Bridge", Windows starts to create
the bridge, and then fails with the error message "An unexpected error
occurred while configuring the network bridge". If I subsequently look
at the right click menu for network adaptors, the option "add to
bridge" has appeared, and adding both adaptors causes the bridge to
appear in Network connections, but with a status of "Network cable
unplugged". (Oh, and neither connection works if I do that...)

The only advice I can find out about this online is to make sure ICS is
disabled before configuring the bridge, but it is already disabled on
all adaptors on this machine. I've tried running the Network Setup
Wizard, but that doesn't even try to bridge the connections. I've tried
a clean install of Windows with no luck, and have pretty much run out
of ideas - any advice gratefully received.

Many thanks in advance.

Simon Long