Bug - Deleting custom number format used in conditional format corrupts Excel file and cannot save

I have encountered the same issue. A file with some Visual Basic code in it the loads a few downloads of data, then pivots the data and creates an automated recon. It worked very well. Until…. I added some conditional formats at one point to make new “refunds” that had not yet been invoiced in our accounting system red, what a big mistake. I’ve tried everything, file corrupts after any save. I’ve even tried cutting and pasting each worksheet into a new file then taking the time to edit the pivot tables etc and it still corrupts. Microsoft won’t bother fixing this, they have other known issues they have ignored. Remember their earlier post on their developer website a couple years after they first released 64 bit office. They said, as a company, they had no intention of making a 64 bit version of Visual Basic that goes with office 64 bit, despite thousands of posts of people using VB in 64 bit office and complaining. If you had only 1 excel file open with VB then cb works ok. If you have 2 or more excel files with visual basic in them, open at the same time, and run the code in them, then save them, then windows will think the files are corrupt when you try to later re-open them. So office also creates endless serious issues for those that want to use automation code.

Excel is a badly needed product, and it has serious bugs that are openly ignored by management.