Insufficient memory to continue the execution of the program

for (int i = 0; i < ltTemplateIndex.Count; i++)
{
    string fileName = Path.Combine(  Path.GetTempPath(),
                                     String.Format(@"template{0}.ppt";
    using (var ppTemp = ppSet.Open(fileName, MsoTriState.msoTrue, MsoTriState.msoFalse, MsoTriState.msoFalse))
    {
        if (i == 0)
        {
            ppMergedPres = ppTemp;
            ppMergedSlides = ppMergedPres.Slides;
        }
        else
        {
            ppPres = ppTemp;
            if (ltTemplateIndex.Count > 1)
            {
                try
                {
                    ppMergedSlides.InsertFromFile(fileName, ppMergedSlides.Count, 1, ppPres.Slides.Count);
                }
                catch (Exception ex) { }
                finally
                {
                    if (ppPres != null)
                        ppPres.Close();
                } 
            }
        }
    }  // Resources will be released here
}
 
string directoryPath = System.Web.Hosting.HostingEnvironment.MapPath("~/Results");
 
if (!Directory.Exists(directoryPath))
    Directory.CreateDirectory(directoryPath);
 
ppMergedPres.SaveAs(
                        Path.Combine(directoryPath, pptFileName),
                        PowerPoint.PpSaveAsFileType.ppSaveAsPresentation, 
                        MsoTriState.msoFalse);
 
ppMergedPres.Close();