Josh,
Not sure if it's related at all since it wasn't in CB, but the other day I was manually creating a instance using my ESRI authorized ami and I changed one of the drive size values and proceeded through the process. Eventually when I went to start the instance I got a error that the instance creation failed because it couldn't find the instance name.
I scrapped that attempt and restarted the creation process without changing any of the default ami settings and creation worked fine.
I don't remember the CB workflow off the top of my head, but if you had changed any default settings I'd try creating another instance leaving everything as is. It seems like it may be a problem somewhere with AWS.
It's kind of a long shot, but maybe it will help.