I only can suppose ... but I think you should change your code like this :
private void Export()
{
SaveFileDialog saveDialog = new SaveFileDialog();
saveDialog.Filter = "Excel files (*.xlsx)|*.xlsx|All files (*.*)|*.*";
saveDialog.FilterIndex = 2;
DialogResult myResult = saveDialog.ShowDialog ;
if (myResult == System.Windows.Forms.DialogResult.OK)
{
xlWorkBook.SaveAs(saveDialog.FileName, Microsoft.Office.Interop.Excel.XlFileFormat.xlWorkbookNormal, misValue, misValue, misValue, misValue, Microsoft.Office.Interop.Excel.XlSaveAsAccessMode.xlExclusive, misValue, misValue, misValue, misValue, misValue);
StripStatusLabel.Visible = true;
StripStatusLabel.Image = Image.FromFile(@"\\90.0.0.8\d\Nouman's Development\SizaPayRoll For Backup\backup\SizaPayRoll\icons\images (3).jpg");
StripStatusLabel.ForeColor = Color.Green;
StripStatusLabel.Text = "Increment export to excel successfully...";
xlWorkBook.Close(true, misValue, misValue);
xlApp.Quit();
releaseObject(xlWorkSheet);
releaseObject(xlWorkBook);
releaseObject(xlApp);
}
else if (myResult == System.Windows.Forms.DialogResult.Cancel)
{
}
}
... because if you get a DialogResult from the SaveFileDialog the SaveFileDialog is no more existing ...
Please try it ...