SqlBulkCopy – The given value of type String from the data source cannot be converted to type

/// <summary>
        /// 
        /// </summary>
        /// <param name="P_str_Excel">excel file name</param>
        /// <param name="P_str_SheetName"></param>       
        public void ImportDataToSql(string P_str_Excel, string DestinationTableName, ColumnMappingCollection collectionMapping, bool ifClearContent = false)
        {
            //DataSet myds = new DataSet();                               //创建数据集对象
            try
            {
                string P_str_SheetName = GetSheetName(P_str_Excel)[0];
                //获得全部数据
                string P_str_OledbCon;
                if (Environment.Is64BitOperatingSystem == false)
                    P_str_OledbCon = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + P_str_Excel + ";Extended Properties=\"Excel 8.0;HDR=Yes;IMEX=2\"";
                else
                    P_str_OledbCon = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + P_str_Excel + ";Extended Properties=\"Excel 12.0;HDR=Yes;IMEX=2\"";
                OleDbConnection oledbcon = new OleDbConnection(P_str_OledbCon);     //创建Oledb数据库连接对象
                string P_str_ExcelSql;                             //记录要执行的Excel查询语句
                OleDbDataAdapter oledbda = null;                            //创建Oledb数据桥接器对象
                P_str_ExcelSql = string.Format("select * from [{0}$]", P_str_SheetName);    //记录要执行的Excel查询语句
                oledbda = new OleDbDataAdapter(P_str_ExcelSql, P_str_OledbCon);     //使用数据桥接器执行Excel查询

                DataTable importedTable = new DataTable();
                importedTable.Columns.Clear();

                oledbda.Fill(importedTable);                            //填充数据

                if (ifClearContent)
                {
                    //清楚非内容行
                    ColumnMapping firstColumn = collectionMapping.FindbyFileIndex(0);
                    List<DataRow> deleteList = new List<DataRow>();
                    foreach (DataRow item in importedTable.Rows)
                    {
                        if (item[0].ToString() != firstColumn.FileFieldName)
                            item.Delete();
                        else
                            break;
                    }

                    int i = 0;
                    foreach (var item in collectionMapping)
                    {
                        importedTable.Columns[i].Caption = item.FileFieldName;
                        importedTable.Columns[i].ColumnName = item.FileFieldName;
                        i++;
                    }

                    importedTable.AcceptChanges();
                    oledbda.Update(importedTable);
                }

                using (SqlBulkCopy bcp = new SqlBulkCopy(ConnectString))         //用bcp导入数据
                {
                    bcp.BatchSize = 100;                                //每次传输的行数
                    bcp.DestinationTableName = DestinationTableName;             //定义目标表
                    foreach (var item in collectionMapping)
                    {
                        bcp.ColumnMappings.Add(item.FileFieldName, item.DataColumnName);
                    }
                    
                    bcp.WriteToServer(importedTable);                      //将数据写入Sql Server数据表
                }
            }
            catch(Exception ex)
            {
                throw ex;
            }
        }

        private List<string> GetSheetName(string P_str_Excel)                           //获取所有工作表名称
        {
            List<string> P_list_SheetName = new List<string>();                     //创建泛型集合对象
            string P_str_OledbCon;
            if (Environment.Is64BitOperatingSystem == false)
                P_str_OledbCon = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + P_str_Excel + ";Extended Properties=\"Excel 8.0;HDR=Yes;IMEX=2\"";
            else
                P_str_OledbCon = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + P_str_Excel + ";Extended Properties=\"Excel 12.0;HDR=Yes;IMEX=2\"";
            OleDbConnection olecon = new OleDbConnection(P_str_OledbCon);                                         //连接Excel数据库
            olecon.Open();                                              //打开数据库连接
            System.Data.DataTable DTable = olecon.GetSchema("Tables");                  //创建表对象
            DataTableReader DTReader = new DataTableReader(DTable);                 //创建表读取对象
            while (DTReader.Read())                                     //循环读取
            {
                string P_str_Name = DTReader["Table_Name"].ToString().Replace('$', ' ').Trim(); //记录工作表名称
                if (!P_list_SheetName.Contains(P_str_Name))                     //判断泛型集合中是否已经存在该工作表名称
                    P_list_SheetName.Add(P_str_Name);                           //将工作表名添加到泛型集合中
            }
            DTable = null;                                              //清空表对象
            DTReader = null;                                            //清空表读取对象
            olecon.Close();                                             //关闭数据库连接
            return P_list_SheetName;                                        //返回得到的泛型集合
        }