So... after trying to setup a subscription yesterday and getting the 601 error with three different cards, I came to this forum to figure out just what I was doing wrong. After reading all these problems and general lack of help people were receiving, I was getting pretty discouraged from attempting any more to continue playing. (which is a total bummer, as I'm really enjoying this game so far.) Anyhoozle, I decided to try once again after waiting the 24 hours. This time before I tried to add a subscription to my account, I registered a payment method first. I don't know if that was indeed a solution, I could have just gotten lucky this time around, but I was able to sign up for a subscription after doing the registration.

Hopefully this helps anyone else who's been having the same 601 problem.