Error converting data type nvarchar to datetime

I have the following procedure interface:

Create procedure [dbo].[InsertItemDetails]
    @TimeItemAdded datetime

When I call it this way:

EXEC [dbo].[InsertItemDetails]
     @TimeItemAdded = N'20/07/2012 00:00:00';

I get this error:

Msg 8114, Level 16, State 5
Error converting data type nvarchar to datetime.