I have the weekend card and this happens regularly when I look for flights that cannot use it - e.g. one ways, intercontinental etc.
even if I remove the card, it just stays attached and does not let me find flights.

the only solution? logoff, find the flight I need and only login when it's time to add my details. will not help for award flights though.

this is certainly not your problem as you're based in the US, but it may easily be some small overlooked detail like this one.