I'm trying to read an Excel (xlsx) file using the code shown below. I get an "External table is not in the expected format." error unless I have the file already open in Excel. In other words, I have to open the file in Excel first before I can read if from my C# program. The xlsx file is on a share on our network. How can I read the file without having to open it first? Thanks

string sql = "SELECT * FROM [Sheet1$]";
string excelConnection = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + pathname + ";Extended Properties=\"Excel 8.0;HDR=YES;IMEX=1;\"";

using (OleDbDataAdapter adaptor = new OleDbDataAdapter(sql, excelConnection)) {
    DataSet ds = new DataSet();
    adaptor.Fill(ds);
}