We had same error. Following code worked for us.
var loadOptions = new Aspose.Slides.LoadOptions();
loadOptions.BlobManagementOptions.IsTemporaryFilesAllowed = true;
loadOptions.BlobManagementOptions.TempFilesRootPath = temp_folder;
using (var ppt = new Aspose.Slides.Presentation(filePath, loadOptions))
{
.....................
}