Yesterday afternoon there was a temporary issue with Google AdWords. A WebmasterWorld thread reported that billing information is temporarily unavailable at about 4pm (EST).
Google said they were aware of the issue and they were working to fix it:
Yep, engineering is aware of the issue you describe, and is hard at work towards resolving it.
I strongly suspect that this'll be seen only by a small percentage of advertisers - and my apology to those who are.
I'll update you all as I learn more.
At about 6:20pm (EST) the problem was resolved. The total issue lasted approximately one hour and thirty minutes.
In addition, the Google Maps Coupon featured is reportedly fixed.
Forum discussion at WebmasterWorld.