When I clicked the edit button of my Hub Group "Economics & Finance" to view what are the topics in it and then wanted to save it as it is, a box splashed saying that the hub group is invalid. I wanted to check which group should I select instead of that invalid group title. But I could not find any default group names. So, I clicked cancel and came out of that interface. So, can any body tell me what are the "allowed groups" for hubpages topics?