I've had several problems like that. Last few have been due to "Backend Server Errors". Wait a bit and try again. It's usually corrected with 12 hours. It also tends to do this while processing some orders, so make sure you don't get double billed for anything if an error pops up mid way. I've had that happen too.
I find Sunday evenings it crashs quite a bit and doesnt get fixed until Monday. They must work monday to friday.
They need to fix there severs, IBM are the tech support for them