I've actually lived through something like that. I was called in to develop a data export from a production database to a system on another platform. I was all ready to go via CSV, but I was specifically told that the export should be in an Excel file.
This was when Office 2010 was already out, so I didn't have much chance of hitting the million row limit.
So I did the job as per spec, created the code that grabbed the data, opened a new Excel sheet and plonked it in, row by row, then saved and closed Excel, grabbed the file and FTP'd it to wherever it had to go.
A few years later I got a call from that same customer. They remembered that I had done the job and now it wasn't working anymore, could I come in and fix the problem ? Sure.
So I went and checked the code. Nothing had changed in my code, so I asked to be able to run a test. With permission I ran the code in debug mode and, lo and behold, when Excel was asked to open a spreadsheet the code halted, there was no spreadsheet to be had.
After explaining the problem, a server admin used his access to check the server in question and reported that Office was no longer installed on the server. Long story short, it turns out that the beancounters were checking lists of Office licenses against users and, since that license didn't have a person associated to it, they cut the license. Apparently it would be useless trying to explain that that license was a business requirement. It was internal procedure that every Office license had to correspond to an actual, breathing human being.
Solution ? Could you please modify the code to use the CSV format ? Sure. That way the recipient will just have to bung it into Excel on his license. Problem solved.
Another day at the coalface.
