Stardoll might be blocked at the moment then. By blocked I mean a LOT of people logging in. There's not much to do. Wait 5 minutes and try again. If not try to contact stardoll. Hope I helped a bit- Kiki7324 (from stardoll)
The code (or phone number) may be invalid. Stardoll stated in the help column; You may have to wait 24 hours before trying a new code or phone number. Stardoll limits the amount of codes and memberships a week.