excel工作簿的自定义文档属性的设置异常

I am working on an excel VSTO add-in, in thie add-in I structure some worksheets to process them later. I want to know later when the user open and excel workbook if the workbook was structured with my add-in or not to do some processing on it. To this end I try to used CustomDocumentProperties.I am working on an excel VSTO add-in, in thie a