This error occurs when the class year group and the key stage entered in the Class Information area is not consistent. Go to the Spring Census front page, then click on Class Details.
Check the entry against the class name which has been identified in the error (in this example, Kiwi Class):
Look at the Key Stage column, and check this against the Year Group selected for the class. Click on the pencil icon to edit the entry. In this example, Year 3 is Key Stage 2. Either the Year Group or the Key Stage needs to be amended. After the change has been made, scroll across to the Actions column and click on the tick to save, then Save again at the base of the page.