Hi Lockwell,
Thank you very much for your suggestions. 
Regardng this formula :SUM({DateTable1.SalesPrice},{DateTable1.MerchantID})
I have tried it earlier and while Click on the Save and Close option it generate this error message:
"A number, currency amount, boolean, date,time, date-Time, or string is expected here."
This is the procedures I have taken to create the Display Field for the Total SalesPrice:
On the Left side of the screen, under the Field Explorer Menu option
- Right Click and select NEW
- Under Create Running Total Field Dialog screen,
select SALESPRICE for the Field to summarize.
- Evaluate
select On Change of Group [ Group #1: DataTable1.MerchantID ]
- Reset
On change of Group [ Group #1: DataTable1.MerchantID
I am very puzzled by the Error Message because the SALESPRICE datatype is MONEY 
The CrystalReport Datasource is from DataSet1.XSD
Edited by Lennie - 16 Mar 2010 at 10:10am