Databases :: Some Of The Cell Value Can't Read From Excel?

Im reading some data from the excel file, using below code

objBusy = new BusinessLogic();
string strFileName = FileUpload1.PostedFile.FileName;
string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=" + strFileName + ";" + "Extended Properties=Excel 8.0;";
OleDbConnection objConn = new OleDbConnection(connectionString);
objConn.Open();
String strConString = "SELECT * FROM [Product1$]";
//where date = CDate('" + DateTime.Today.ToShortDateString() + "')";
OleDbCommand objCmdSelect = new OleDbCommand(strConString, objConn);
// Create new OleDbDataAdapter that is used to build a DataSet
// based on the preceding SQL SELECT statement.
OleDbDataAdapter objAdapter1 = new OleDbDataAdapter();
// Pass the Select command to the adapter.
objAdapter1.SelectCommand = objCmdSelect;
// Create new DataSet to hold information from the worksheet.
DataSet objDataset1 = new DataSet();
objAdapter1.Fill(objDataset1, "ExcelData");

after this if i looks on the DataSet i see some of the cell value not read from the Excel file, what was the problem and how to resolve this?