https://userapps.support.sap.com/sap/support/knowledge/en/2761692
2761692 - Error "Balance of WBS XXXXXXX.X.X is not zero" when changing the stage of an internal...
When changing the Stage of an internal project from 'Completed' to 'Closed', the error "Balance of WBS XXXXXXX.X.X is not zero" is raised.