Here's one that's at the intersection of my fields: tech and music.
I bought a new virtual instrument (Wave Alchemy's Evolution) that happens to use Native Instruments Kontakt as the platform. For those not familiar with electronic music production, Kontakt is a synth platform that runs on your computer that other people can create instruments with. It's also a fine sampler. Native Instruments (the company that makes it) makes buckets of money with this stuff. But I digress!
So I bought this new instrument and it just was NOT showing up in the library section of Kontakt. However, if I ran Kontakt as an admin, it did show up. Well, unfortunately, in the music business it's not uncommon for users to run as admin all the time because the developers and users of these products sometimes have a poor understanding of the Windows security model being this is a Mac-first industry. And musicians, god love them, just want stuff to work, they aren't going to troubleshoot it. So admin all the time it is.
But not me. I can't go against the very core of my nature with regard to IT security! It just feels *wrong*.
So I fired up ProcMon.exe to see what's going on. I mean it has to be a permissions thing right?
Well this one was easy. After filtering on the Kontakt exeutable and searching for "access denied" I found an interesting file. The file "C:\Program Files\Common Files\Native Instruments\Service Center\NativeAccess.xml" was showing as "access denied." I tried to open the file and was denied. So I looked at the properties and saw it had exclusive (non-inheriting) permissions that only allowed SYSTEM and Administrator access. No other file in the folder did that, so I'm going to assume this is a mistake/bug/whatever. And previous instruments I bought always installed okay, so maybe this only happened after an NI update? Not sure.
The file looks like it's just a master record of everything installed from Native Instruments, so that would make sense that if a normal user couldn't see that, they couldn't see newly installed instruments (presumably the other instruments' installation are cached in the per-user data somewhere).
So, I reset permissions on that file, allowing inheritance, and now it works.