This message is displayed by some functions when the number of forecasting periods is not the same in each year.
This can be caused by the 'Forecast start month of the year' field being changed in the parameters. In older versions of Demand Forecasting it can be displayed even when the number of periods is the same, but the 'Forecasting period mode' field in the parameters has been edited but not changed.
To resolve the problem, manually select and delete all records in the Forecasting periods form on the Setup menu, and then use the 'Create forecasting periods' button on the screen to recreate them.