The issue is not Foobar-related, and there are no "problematic FLAC files".
The errors are reported ONLY when I open MB. After that MB works properly.
It is related to this plugin, because when the plugin is disabled, there's no error.
I have no problem tagging with MB, and foobar. I use them interchangeably, according to what I need.
The plugin informs me that it didn't initialize properly, but I can't say what it means.
I tried to use the library reports, and it seemed to have worked fine.
The foobar versions varied over time from 1.2.1 to 1.2.6 to the latest beta 1.2.7.
The metaflac.exe is the same as far as I know. Only the FLAC was lately upgraded, and again, it's irrelevant here.