Do you have that file (resume.xlw) open in another window while you're running your script? The reason being is that I think MsExcel.Save() (if MsExcel is an instance of the Excel.Application object) sends the "Save" command to the application in general rather than the specific document you're working on.
Try closing out all Excel windows you have open and rerun.
Also, it might be helpful for you to post the code or a sample code of what you're doing to write to and save the excel file so we can perhaps debug further.