How to read a value from SAP DBDataSource

I am trying to read row values from the sales order - items matrix

I tried this code

Dim dbdata As SAPbouiCOM.DBDataSource

dim strItemCode as string

dbdata = oform.DataSources.DBDataSources.Item("RDR1")

stritem = dbdata.getvalue("ItemCode",1)

but I am receiving in error -2010

Error Desc: Data soruce - Bad Data Source Offset

sincerely yours

Riade Asleh