一个奇怪的问题

   我想把Excel表中的数据导入到Access数据库中.Excel表有4个sheet,Access中对应4个数据表,用相同的代码前三个表我已经成功导入,可是最后一个表一直提示:"insert into 语句的语法错误".我用断点调试查看insert 语句语法根本没有错误啊,真是奇怪,附部分代码如下,请各位大侠帮忙想想办法啊!
            try
            {
                OleDbConnection cnn_excel = new OleDbConnection();
                cnn_excel = conn_excel(dbpath);                   //excel的conn
                OleDbConnection cnn_access = new OleDbConnection();
                cnn_access = conn_access(dbname);                //access的conn
                string strsql_excel = "";
                string strsql_access = "";
                DataTable dt = new DataTable();                  
                strsql_excel = "select * from [" + tablename + "$]";
                strsql_access = "select * from " + tablename;
                OleDbDataAdapter da_excel = new OleDbDataAdapter(strsql_excel, cnn_excel); //建立excel的dataset数据集
                DataSet ds_excel = new DataSet();
                da_excel.Fill(ds_excel);
                dt = ds_excel.Tables[0];
                OleDbDataAdapter da_access = new OleDbDataAdapter(strsql_access, cnn_access);//建立access的dataset数据集
                DataSet ds_access = new DataSet();           
                da_access.Fill(ds_access);
                DataTable dtaccess = new DataTable();          
                dtaccess = dt.Copy();
                dtaccess.TableName = tablename;
                ds_access.Tables.Add(dtaccess);
                for (int i = 0; i < ds_access.Tables[tablename].Rows.Count; i++)
                {
                    string strinsertaccess1 = "";
                    string strinsertaccess2 = "";
                    string strinsertaccess = "";
                    switch (tablename)
                    {
                        case "table1":
                            strinsertaccess1 = "insert into " + tablename + "(字段1,..) values(";
                            break;
                        case "table2":
                            strinsertaccess1 = "insert into " + tablename + "(字段1,..) values(";
                            break;
                        case "table3":
                            strinsertaccess1 = "insert into " + tablename + "(字段1,..) values(";
                            break;
                        case "table4":
                            strinsertaccess1 = "insert into " + tablename + "(字段1,..) values(";
                            break;
                    }
                    for (int j = 0; j < ds_access.Tables[tablename].Columns.Count; j++)
                    {
                            if (j == 0)
                            {
                               strinsertaccess2 += "'" + ds_access.Tables[tablename].Rows[i][j] + "'";
                            }
                            else
                            {
                              strinsertaccess2 += ",'" + ds_access.Tables[tablename].Rows[i][j] + "'";
                            }
                    }
                    strinsertaccess= strinsertaccess1+strinsertaccess2 + ")";
                    OleDbCommand cmd_exceltoaccess = new OleDbCommand(strinsertaccess, cnn_access);
                    cmd_exceltoaccess.CommandText = strinsertaccess;
                    cmd_exceltoaccess.ExecuteNonQuery();
                    cnn_excel.Close();
                    cnn_access.Close();
                }
                MessageBox.Show("添加数据表"+tablename+"成功!");
            }
            catch (Exception ee)
            {
                MessageBox.Show(ee);             
            }