I've been using the Rio-supplied HPNA card since I got mine, which should be close to a year now, with no problems at all.

Sorry if what follows seems a bit obvious...

Do you use an analog modems? Have they been failing on you too? Is there anything unusual about your phone setup? If so, a surge protector would be a good idea. If not...

Are you sure the HPNA card went bad? Did you try pulling the card, uninstalling/reinstalling the driver and reinstalling the card?