This error arises due to the Department for Education (DfE) not accepting certain class activities for students in Key Stage 1 or Reception class. Head to the front page of the Spring Census and click on Class Details.
Check the Activity column for the class identified in the Error (in this example, Banana Class).
For classes in Key Stage 1 or Reception Class, the DfE will not accept Activies of : 'PE or Games', 'Watching TV', or 'Music Singing or Drama'. Click on the pencil icon to edit the entry, selecting another option ('Other' is an option if none of the choices feel appropriate). Save the entry by clicking on the tick in the Actions column, then recalculate the Spring Census.