If you have reached the limit for creating active classes you have a couple of options:
Archive any unused classes you might have
If you can, archive any old or unused active classes. Archived classes do not count towards your class limit and can be unarchived at any time. In most situations this should fix the problem.
Contact us to increase your active classes limit
If you have a real need to create and teach with more active classes than the limit allows you can email email@example.com and we should be able to help you out, or at the very least give some guidance.