Excel truncated

From time to time I look at an Excel file and find only the Excel header, with one column name and its value but no columns. The file has so far alwasy been created within Access using the common dialog; the user is allowed to see and edit the file as an Excel application from within Access, and no problem occurs there. The usual pattern of my tests has been to create and fill and inspect two such Excel files in a run; when I then open each from a folder window one of them is sometimes truncated as I have described.