How to draw line after each group in SSRS .

See more:

SSRS

I did group by account number in ssrs Table . Now i want when the account number group will be end the horizontal line will be come ..


for eg :

AccountNumber:1000
1 . 100% European Opportunities Series DBT
2. 100% Securitized Assets Fund (Delaware) L.P.
-------------------------------------------------------------
AccountNumber:2000
1 . 100% European Opportunities Series DBT
-------------------------------------------------------------

In the above example in 1st group i am shoiwng two records then line in second group i am showing 1 records then line

What I have tried:

Select entire group row then press f4 .
Go to borderstyle property ->Go to Top->put below expression

=Iif(Fields!AccountNumber.Value = Previous(Fields!AccountNumber.Value) OR Fields!AccountNumber.Value = First(Fields!AccountNumber.Value, "AllocationHistory"),"None","Solid")

i got this error mentioned below : 
[rsInvalidAggregateScope] The BorderStyle expression for the text box ‘AccountNumber’ 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.