You may have too many cell formats/styles. To see if that's possibly true,
click on the Cell Styles "More" arrow and see if you have a gazillion styles
showing. If that's true, you can remove unused styles by saving the workbook
as a web page, closing, reopening, save as a normal workbook.

"Chrystopher" wrote:

An Excel 2007 file (e.g. File.xlsx) loses its formatting when it is reopened.