Show/Hide in Subform

Show/Hide in Subform

Hi,
I want to hide/show the fields inside the subform. Hide works perfectly on load but show action doesnt work it says "Invalid task in Subform action".

Code:

if(Job_Work_Challan.Accessories = "Cartons")
{
show Job_Work_Challan.Quantity ;
show Job_Work_Challan.Dimensions_Cartons ;
}

wherein 
Job_Work_Challan = subform
Accessories = checkbox
Job_Work_Challan.Quantity & Job_Work_Challan.Dimensions_Cartons = Both single line fields which i want to show.