It would help to know where the exception is thrown but a section of the code doesn't look right.
private void getExcelData(string get_File)
{
FileStream F_stream = File.Open(get_File, FileMode.Open, FileAccess.Read);
_Excel_App = new Excel_ref.Application();
_curr_WorkBook = _Excel_App.Workbooks.Open(openFileDialog1.FileName,
0, true, 5, "", "", true, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows,
"\t", false, false, 0, true, 1, 0);
1) Remove the File.Open because you want Excel to open the file.
2) Replace openFileDialog1.FileName with get_File.
Alan.