The PowerSchool Community is a great resource if you have any changes to be made while completing fields within the enrollment form. Each district, however, has a different registration process and can provide the best steps to move forward when enrolling students.
This error usually occurs if the student records are not notified or put on hold at the district end when maintenance is being done. One of our Community members faced a similar issue and the resolution was provided within this thread. I recommend reviewing the resolution provided.
You can check out the FAQs related to the enrollment process here.