Same thing happened to me recently. My existing Gold subscription expired, and I tried to buy another month on my console. It froze up, I shut it down and tried again, same result.
Figured I'd try buying through Xbox.com and got the error code you did. My credit card has been charged, though. I contacted live chat and the guy had me do everything imaginable - erasing and redownloading my profile, clearing the system cache, resetting network preferences, removing and reinserting the HDD, etc. No luck. Now they say they'll contact me within 10 days.