=IF(ISERROR(FORECAST(COLUMN(),$AF4:AH4,(COLUMN($AF 1:AH1)))),"",FORECAST(COLUMN(),$AF4:AH4,(COLUMN($A F1:AH1))))

I have this formula in my worksheet but a message box pop up
......The formula you type contains error and it highlights the formula ""


do i miss something here? thanks for any help, I appreciate.