How do fix RDLC report grouping not giving correct sum in textbox

I grouped my report based on customer_status and transaction_id, the report is fetching quite Owk. the problem am facing when I tried to sum the total column of grand_total, it doesn't give me the actual Summation, it double sum the first customer row which is (18,700) to 37,400 and plus the second row which give (54,400). My calculations was to be (35,700)

My grand_total feild =fields!grand_total.Values 

My sum grand_total column
=Sum(CDec(fields!grand_total.Values), "DataSet1"). because I have two(2) datasets

=Sum(CDec(fields!grand_total.Values), "DataSet1") =Sum(CDec(First(fields!grand_total.Values)), "DataSet1") Displayed error of type there is an inner aggregation. =Sum(Max(CDec(fields!grand_total.Values)), "DataSet1") Same error as above =Sum(CDec(fields!grand_total.Values, "grand_total"), "DataSet1") error =Sum(CDec(fields!grand_total.Values),"grand_total", "DataSet1")

It keeps on showing (TextBox) has an inner aggregate in an outer aggregate that specifies a dataset scope. An aggregate that specifies a dataset scope cannot contain other aggregate