The "Registration is not active" is shown when there are no active categories that people can register for, or if the current date and time are outside of the registration period for the program.
If there's a "Registration is not active" message on your registration form, please check the following:
in Settings > Program > Program basics make sure the Accepting registrations period is active.
in Settings > Categories see if your program categories are set to Hidden status. For the program registration to be active you need at least one category set to Public status.
if your program is on a pricing plan with an application limit, check the Dashboard to see if it has been reached. If you wish to accept additional applications you can upgrade your plan by pressing the Upgrade button there.