
I had an interesting issue creep up a bit ago with Excel files that were created by a web application not opening in Excel.
I had a ColdFusion app that would generate reports on the fly for users. We were using CFHEADER and CFCONTENT to deliver table formatted data as XLSX files. It had been working fine right up until it didn't. We hadn't made any changes to the code and checked and confirmed that there were no changes/patches ...