异常：没有为命令对象设置命令

OleDbConnection oleConn = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + Application.StartupPath + @"\MIEDataBase.mdb"); 
            oleConn.Open(); 
            
            OleDbCommand AICmd = new OleDbCommand(); 
            AICmd.Connection = oleConn; 
            
            OleDbDataAdapter AIOleDbDataAdapter = new OleDbDataAdapter(); 
            AIOleDbDataAdapter.SelectCommand = AICmd; 
            DataSet AIDataSet = new DataSet(); 
            OleDbCommandBuilder AIOleDbCommandBuilder = new OleDbCommandBuilder(AIOleDbDataAdapter);             AIOleDbDataAdapter.Fill(AIDataSet, AItableName);             DataRow AIRow = AIDataSet.Tables[0].NewRow(); 
            float AItimeOfEveryData = 0;             for (int i = 0; i < countOfDataNeededToStore; i++) 
            { 
                AIRow["模拟量时间"] = Math.Round(AItimeOfEveryData, 5); 
                AIRow["MP1"] = Math.Round((float)mcMP1arrayy[i], 2); 
                AIRow["MP2"] = Math.Round((float)mcMP2arrayy[i], 2); 
                AIRow["MP3"] = Math.Round((float)mcMP3arrayy[i], 2); 
                AIRow["MP4"] = Math.Round((float)mcMP4arrayy[i], 2); 
                AIRow["MP5"] = Math.Round((float)mcMP5arrayy[i], 2); 
                AIRow["MP6"] = Math.Round((float)mcMP6arrayy[i], 2); 
                AIRow["MP7"] = Math.Round((float)mcMP7arrayy[i], 2); 
                AIRow["MP8"] = Math.Round((float)mcMP8arrayy[i], 2); 
                AIRow["MP9"] = Math.Round((float)mcMP9arrayy[i], 2); 
                AIRow["MP10"] = Math.Round((float)mcMP10arrayy[i], 2); 
                AIRow["MP11"] = Math.Round((float)mcMP11arrayy[i], 2); 
                AIRow["MP12"] = Math.Round((float)mcMP12arrayy[i], 2); 
                AIRow["MP13"] = Math.Round((float)mcMP13arrayy[i], 2); 
                AIRow["MP14"] = Math.Round((float)mcMP14arrayy[i], 2); 
                AIRow["MP15"] = Math.Round((float)mcMP15arrayy[i], 2); 
                AIRow["CF1"] = Math.Round((float)mcCF1arrayy[i], 2); 
                AIRow["CF2"] = Math.Round((float)mcCF2arrayy[i], 2); 
                AIRow["JJY"] = Math.Round((float)mcJJYarrayy[i], 2); 
                AIDataSet.Tables[0].Rows.Add(AIRow);                 AItimeOfEveryData += AICaiYangZhouQi;             }             AIOleDbDataAdapter.Update(AIDataSet, AItableName); 
            AICmd.Dispose(); 
            AIOleDbDataAdapter.Dispose(); 
  执行这一句  AIOleDbDataAdapter.Fill(AIDataSet, AItableName);异常：没有为命令对象设置命令。 什么原因呀