在DataView中排序异常

我有c#代码，我从中得到一个异常:

" GetCurrency中针对货币代码(USD)的异常":系统。Find根据排序顺序查找行，并且没有指定排序顺序。在System.Data.Index。FindNodeByKey(Object originalKey)System.Data.Index。FindRecordByKey(对象键)"。

请查看我的代码，并告诉我为什么我得到这个异常:

public static DataView curInfoView= null;
public static string GetCurSymbol(string curCode)
{
    string curSymbol = string.Empty;
    if (string.IsNullOrEmpty(curCode))
       return curSymbol;
    try
    {
        curInfoView = new DataView(curInfoDataSet.Tables[0]);
        if (curInfoView != null)
        {
            curInfoView.Sort = "CurCode Asc";                    
            int rowIndexCurrencyInfoView = curInfoView.Find(curCode_);
            if (rowIndexCurInfoView > -1)
            {
                // initialize large currecncy
                DataRowView drCurInfo = curInfoView[rowIndexCurInfoView];
                curSymbol = Convert.ToString(drCurInfo["CurSymbol"]).Trim();
            }
        }
    }
    catch (Exception ex)
    {
        AppLog.Log("Exception in GetCurrency For Currency Code ( " + curCode_.ToString() + ") :" + ex.ToString());
    }
    return curSymbol;
}

curInfoView.Sort = "CurCode ASC";