Periodically (often as developers, sometimes as users) Excel fails to load custom functions for various reasons and shows this error:
It would be really, really helpful if the UI error said what functions couldn't be loaded and why (perhaps via a "Details" button/link). As a developer, I know how to enable and then look in AppData\Local\Temp\1\OfficeAddins.log.txt (although it seems to me it only sometimes has any relevant information), but end users don't, and it's hardly convenient.