A cláusula ORDER BY é inválida em exibições, funções embutidas, tabelas derivadas, subconsultas e expressões de tabela comuns

Você não precisa usar ORDER BY na consulta interna após WHERE cláusula porque você já a usou em ROW_NUMBER() OVER (ORDER BY VRDATE DESC) .

SELECT 
    * 
FROM (
    SELECT 
        Stockmain.VRNOA, 
        item.description as item_description, 
        party.name as party_name, 
        stockmain.vrdate, 
        stockdetail.qty, 
        stockdetail.rate, 
        stockdetail.amount, 
        ROW_NUMBER() OVER (ORDER BY VRDATE DESC) AS RowNum  --< ORDER BY
    FROM StockMain 
    INNER JOIN StockDetail 
        ON StockMain.stid = StockDetail.stid 
    INNER JOIN party 
        ON party.party_id = stockmain.party_id 
    INNER JOIN item 
        ON item.item_id = stockdetail.item_id 
    WHERE stockmain.etype='purchase' 
) AS MyDerivedTable
WHERE 
    MyDerivedTable.RowNum BETWEEN 1 and 5