Twice in a row we had the Costco 2 lb cheddar block go really nasty on is. It was fairly quick too, so we don't buy it anymore.
Aw, sorry that happened to you, justajane, but it can happen to cheese purchased just about anywhere. The good news is that Costco will refund your money, no questions asked. You don't need to bring in the gross cheese, just the package should suffice. They can look up your purchase on your card, so you don't even need a receipt...
Re: Freezing Cheese
Yes, cheese can be frozen, but it changes the texture somewhat. Best approach is to grate it onto cookie sheets, flash freeze, then store in your favorite freezer safe vessel(s). Keeps well and defrosts quickly. Whole blocks of cheese tend to be crumbly after freezing :-((