Building an IIF statement with a Yes/No Field

I'm trying to do a calculation to refer back to a field if another field =Yes and I keep getting the #Type! error. The fields are [Written] which contains a currency total, [LR Test] which is the Yes or No field and [Written totals]. So basically what I want my expression to do is IF LR Test = Yes I want Written Totals to show the amount from the [Written] field, IF it's a No, then it could be Null or 0.

This is the calculation I have tried that returns with #Type! IIf(([LR Test]=Yes),[Written],Null)

Any help or advice is greatly appreciated. I'm very new to access so it has been quite a struggle.