I have this same problem now and to be honest, this also happened the last time i wanted to buy a game.
The last game i bought, i wanted also to buy in the WEEKEND, but it kept failing, didnt matter if i used creditcard or paypal.
That game i could buy later midweek, so i though, that it was just an incident.
Now i wanted to buy democracy and it didnt let me buy it either and guess what, its again weekend!
Well, i am not sure if i am gonna buy it next midweek, i was hoping to play it in the weekend.
If you dont want your customers to buy in the weekends, that place make that clear.
Its really irritating to keep filling in correct info and getting nonstop messages, that it cant be confirmed and you have to try another payment methode.
For me its, clear, somehow in your checking control, they dont work in the weekends................