I set up a user form to control user inputs into a complex workbook. On closing the form a range of inputs are pasted into the book, but because the calculation method is set to Automatic, excel re-calculates the sheet after each value is pasted

When I tried to switch off automatic recalculation in code I get a run-time error which I didn't expect. I used

Application.Calculation = xlCalculationManua

but get the error

Run Time Error 1004 - Method 'Calculation' of object '_Application' faile

Any suggestions as to what causes this and how I can fix it ?