Invalid CDKey

Humble Bundle support should be contacted.

HumbleBundle support.

Humble, since they are the "reseller".

Also try waiting a few hours to a day. Steam will lock you out from activating keys for a while after you activate a few games (just like it'll lock you out from activating any keys after a few duplicates).

Silly question, but have you tried copying the key again, maybe you missed a letter?

Are you typing out the keys or are you copy+pasting them? If you are typing them you might want to try copy+paste since there is a chance of you goofing up a letter or number in the key.

Other than that.. as others have said.. contact HIB's support.

Who cares, support charity and throw them keys away! Cos it's apparently illegal to give them away to others...