At the moment you don't do any aggregation at all so
GROUP BY
clause seems unnecessary. Either remove it
DataFilterQuery = "Select pi.itemname, pi.goldweight, pi.stoneweight, pi.nos " & _
"From (pledgeritem pi Inner Join pledger p On pi.pledgeno = p.pledgeno) " & DataFilterCondition & " Order By pi.itemname"
or add desired aggregations in the statement, for example something like
DataFilterQuery = "Select pi.itemname, sum(pi.goldweight), sum(pi.stoneweight), sum(pi.nos) " & _
"From (pledgeritem pi Inner Join pledger p On pi.pledgeno = p.pledgeno) " & DataFilterCondition & " Group By pi.itemname Order By pi.itemname"