'Sales Discount' KPI shows an exception as, 'Invalid KPI'. Why?

'Sales Discount' KPI shows an exception as, 'Invalid KPI'. Why?

The KPI's definition must have got altered. There will be an issue with the metadata related to the KPI like Measures/Dimensions. You can alternatively check for the KPI validity from Administrator --> KPI Management and verify measure/dimension/filter validity and take corrective action.