How to draw line after every group in SQL Server Reporting Services

I have created 2 group 1 Product Id and 2 prodct name
in one product their can be multiple Items
its Bill of material

PRODUCT PRODUCT NAME ITEM                              BATCH SIZE   BATCH UOM
ID      AND          DESCRIPTION
        Item Name
101001  Punjabi Dal Tadka                                      100 KGS
        302010      Paneer
101002  Lucknowi Rajma Masala                                  220 KGS
        301009      Rajma
        302001      Sunflower Refind oil
        302007      Milk
        302007      Milk
        303001      Ajwain
        303004      Cardamom (Big/black)

so i want to put or draw a line after each product id ends

=Iif(Fields!productid.Value = Previous(Fields!productid.Value) OR Fields!productid.Value = First(Fields!productid.Value, "mydataset"),"None","Solid")
i tried but its not getting proper result

I get this error

The BorderStyle expression for the text box ‘prod_name’  has a scope parameter that is not valid for an aggregate function.  The scope parameter must be set to a string constant that is equal to either the name of a containing group, the name of a containing data region, or the name of a dataset.

Tags: SSRS