Cant buy humble bundle(only one purchase per account?)

That's not true. You can buy multiple copies of their bundles with the same paypal account (source: I did it). What happened here is probably their "anti-reseller" protection kicking in, basically meant to prevent you from hoarding keys from the bundle to resell on the grey market, so you can't order too many bundles in a short timespan.

I have bought 2 tier 2 and 3 bundles twice in past occasions one for myself, second for friends or GA's. I know you can at least get 2 from first hand experience, what you cant do, as far as im concerned is to buy the monthly bundle twice or more with the same account.

What i think what happened is that you bought bundle 1 for your account (and WITH your own HB account) second one you logged in to your brother HB account and tried to purchase with the same paypal account.

What you should do is to buy from your own HB account your first bundle, then buy the second and third one from the same account, but as a gift. In the FAQ on H

So i guess the system detected multiple purchases from multiple accounts with the same Paypal , and automatically locked you out for potential re seller if the scenario i predicted in fact happened..

Both.

I first had this problem at the Capcom bundle

I believe the standard Humble cap is 3 bundles, though I've never tested past that, either.

Really sounds like you just tried to buy too quickly, and- much like how forums have automatic blocking of similar messages shortly after you post a message- blocked your request in case it was accidental [or for illicit resale purposes, as an alternative interpretation].

Another alternative is, since it says 'purchase requests', you may have hit page refresh too many times on the purchase, which would definitely kick in the accidental/spam-purchase protection.