humble bundle help

Dunno, but have a bump so you could have some help! ;)

For your credit card, it could be because you are making a purchase outside your country.

Different Humble Bundles have different purchase limits decided by devs / publishers of games featured. Some bundles you will be able to buy in 5 copies, some in 2. It is done so to fight reselling of bundle content. So the error you get is normal, you reached the limit.

As for CC there may be many issues. Not matching your IP country, being from restricted country, being from restricted operator (HB does not accept many prepaid operators, at least from my country). Try different card, get another one, get prepaid card, set up alt paypal account using another card or bank account and make new purchase with new PP on new humble account, or just accept the fact that bundle purchases at HB are limited ;)