I had a quick look at Diana's problems on the MO2 discord, since the problem seems to have coincided with a new development build from a few days ago.
The most telling test we did was to just start BethINI, then click "Default". The Skyrim.ini file then becomes a pristine copy of Skyrim_Default.ini, which doesn't look right to me. Looking at the code `Spin()` should at least be writing `sLocalSavePath` and a couple more things right after the `FileCopy`. It seems to eventually call `refreshGUI()`, which changes the `uGridsToLoad` widget, which should be picked up in BethINI.ahk to write `uGridsToLoad` under `[General]`.
None of that is happening. The consequence of course is that `FixINI()` then tries to readback `uGridsToLoad`, fails, and then logs the message and displays a dialog.
So it looks like the `FileCopy` succeeds, but the subsequent `IniWrite` fail, which I can't explain. This is complicated by the fact that BethINI has no error checking for writes, making this difficult to diagnose. It's also unclear as to why this started happening in the past few days. I'm not aware of any recent changes to MO2 that could have caused this, but I'll keep an eye out.