Code is something like this.

There is manual excel formating in UltraGridExporter events with setting up formats like this

private void InitializeSum(object sender, Infragistics.Win.UltraWinGrid.ExcelExport.InitializeSummaryEventArgs e)
{
e.ExcelFormatStr = e.Summary.SourceColumn.Format;
}
private void InitializeColumn(object sender, Infragistics.Win.UltraWinGrid.ExcelExport.InitializeColumnEventArgs e)
{
e.ExcelFormatStr = e.Column.Format;
}

//But general code:

//Opening existing xls file
Workbook oWorkBook = new Infragistics.Documents.Excel.Workbook();
oWorkBook = Workbook.Load(xlsFilePath);
if (oWorkBook.IsProtected) oWorkBook.Unprotect(password);

//removing sheet by name if exists and then adding new one with same name
if (oWorkBook.Worksheets.ToList().Select(x => x.Name == newSheetName).Count() > 0)
{
for (int i = 0; i < oWorkBook.Worksheets.Count; i++)
{
if (oWorkBook.Worksheets[i].Name == newSheetName)
{
oWorkBook.Worksheets.RemoveAt(i);
}
}
}

oWorkSheet = oWorkBook.Worksheets.Add(newSheetName);

//doing some manual formating in events and adding export data from filled Ultragrid to newly added worksheet
UltraGridExcelExporter ugrdReport;
ugrdReport = new Infragistics.Win.UltraWinGrid.ExcelExport.UltraGridExcelExporter(this.components);
ugrdReport.HeaderRowExporting += new Infragistics.Win.UltraWinGrid.ExcelExport.HeaderRowExportingEventHandler(HeaderRowExporting);
ugrdReport.SummaryRowExporting += new Infragistics.Win.UltraWinGrid.ExcelExport.SummaryRowExportingEventHandler(SummaryRowExporting);
ugrdReport.InitializeColumn += new Infragistics.Win.UltraWinGrid.ExcelExport.InitializeColumnEventHandler(InitializeColumn);
ugrdReport.RowExporting += new Infragistics.Win.UltraWinGrid.ExcelExport.RowExportingEventHandler(RowExporting);
ugrdReport.BandSpacing = Infragistics.Win.UltraWinGrid.ExcelExport.BandSpacing.None;
ugrdReport.InitializeSummary += new EventHandler<InitializeSummaryEventArgs>(InitializeSum);
ugrdReport.SummaryCellExported += new Infragistics.Win.UltraWinGrid.ExcelExport.SummaryCellExportedEventHandler(ugrdReport_SummaryCellExported);
ugrdReport.ExportFormulas = false;

ugrdEEZurnals.Export(myUltragrid, oWorkSheet, 4, 0);

//setting up file write protection passowrs
oWorkBook.SetFileWriteProtectionPassword(password);

//And saving
oWorkBook.Save(xlsFilePath);

I am following up to inform you that I am working on your case and will have our engineering staff to look at it. I am hoping to have a solution before end of day today.

Thanks.

I created a sample using the code provided, but failed in reproducing the issue. Instead of using Stream to open the file, I directly opened it to the WorkBook from the file.
I am attaching my sample here.
Please let me know if you need any more assistance on this case.

Thanks,
Josheela

Thank You very much will check sample. 

Hi Andris,

There is always that one machine eh!  If the environment matches the other machines this certainly is odd.  What differences exist between the machine that isn't working and the others that do work?  Would this other machine have a different version of the Infragistics tools being used or installed?  Is the sample Josheela added reflective of what you are doing in your application?  Does the sample work locally for you and what happens on the problematic machine?