I have this same issue.
It takes $1 from my account(to ensure the account is real, and that my info was correct), then I get error 401. Now I just get error 601, so it doesn't even accept my information.
I had this issue last time I tried adding my card(roughly 3 weeks ago), so it's an issue on their end, not yours. Last time it happened, I was able to add my card a couple days later. I was never told why it happens, my guess is high traffic.