The most likely reason that this error is occurring is because the currently active school year is not set to be published. The reason this error occurs is because this report allows you to pick which school year to run it for and will by default set the currently active year as the year in the drop down. When the year is not published, it will not be an option from the drop down and results in the error. To fix this we will:
  1. Go to Core > School > Years & Terms
  2. For the Current Year, click the Edit button to the right
  3. In the pop-up change the Publish toggle to Yes
  4. Click Save & Close