I've sent out a few friend keys (not on this account, errm maybe on ntli and another, anyway) One has not been accepted by the receiver cos they tried to apply it to an account that they had paid for in the past. This key is not useless, a new player could still use it (I've given out all my keys to newbs I think, except one it seems) but I have no way to re-issue it, so this is my suggestion/fix.

If a friend key has not been applied within 30 days, credit it back to the issuing account, as long as they are not already over quota on keys.