It can be a ban but can also not be one. Even on a Gateway, Monster Hunter give this error until you change the "Manufacturer" name in the Gateway patcher and then, it works fine (it's a known problem with this game).
Problem is I'm not sure you can change the manufacturer on a Sky3DS (but if someone now how to edit the header, he'll probably answer here).
First, try another online game to see if it's working? (If yes, it's not a ban).
If you are not banned, best thing would be to contact Sky3DS to ask them if they can fix that (you can said to them what I written upper, the thing about the "Manufacturer" problem that also happen on Gateway).