@Colin,
Well, I got info on that *nefarious* error message which *kind of*

clears it up...
Reply 1: Support article by Microsoft which makes mention to the backwards compatibility between Access 2007 and Access 2010 in one section...
https://support.office.com/en-us/ar...n-access-2c498459-100a-4e7f-9e77-657a9423af74
Reply 2: Sort order for new databases affects the file format. It is not just for band new databases though, it impacts the database you are in during compact and repair. So to change sort order, set what you want, then compact and repair.
To install an add-in, it has to be General. Once the add-in is installed, you can change it.
To import data in an older format, it may need to be General-Legacy.
Reply 3: The wording for the option is misleading, it doesn't make it clear that it will apply to existing databases when compacted.
However, I know that the motivation for providing a new sort order was that some scripts were sorting incorrectly, either because characters were either missing, or not in the proper sequence in our 'alphabets'.
I would suggest using General in all cases these days, since Access 2007 is no longer supported, so there is no reason to use the older sort order.
And while I *get it* now that error message would most certainly make no sense to the average User and it is one I had not seen before this thread. And, this might be because I always used *General* and skipped using Access 2007 for development. I only use it for testing if a Client has it.