Firek: Sorry about not replying to your original ticket - I've just sent you a reply to your new ticket, with some information about your current predicament.
As for the purchase limit - there are some speed limits set on our payment processor's end, but on our end we're only limiting gifting. These were not the cause of your payment problems, which we are investigating to the best of our ability.
Unfortunately we haven't been able to recreate the problem yet, as it appears to be randomly occurring. Clearing your cache and cookies - as well as making sure that you aren't running any software that might be modifying the cookie files - might help. I apologize for any inconvenience caused.
Gnostic: I don't know if that is the problems of the cookies, because I do a series of purchase as fast as I can. If there are problems with my cookies I would not be able to buy the first few games purchase. But I do not know well enough to be sure.
For instance this morning I buy Starpoint Gemini and its DLC and succeed
Immediately after I try to buy 5 games as a gift and succeed
Immediately after I try to buy another 5 games as a gift and succeed
Immediately after I try to buy another 6 games as a gift but failed.
Not long ago I see System Shock is available and recommended by JudasIscariot.
So I try buying it and succeed.
Immediately after I try to buy the 6 gift that failed earlier and succeed.
Immediately after I try to buy the second copy of System Shock but failed.
So I wonder if it is the gift purchase limit as mention as Grargar, because my problem happens when I am trying to buy gifts.
This to me sounds like fraud prevention on either the processors part or possibly the cards issuer.
Possibly if you wait a bit between purchases, the issue won't happen.