Permissions error sorting files into new folders

[Florian]

@Arbiter

Am I using the %_workingpath% parameter incorrectly?

Yes, it's not existent on the Mac and resolves to the empty string. See this topic from the documentation for a list of available placeholders:

Format Strings and Available Placeholders

Mp3tag uses format strings in various of its features to describe the structure of file names and imported data. A format string is built of either standard text (e.g., Music), placeholders (such as %artist%, %title%, ...), or slash characters / that usually denote directory structures. Characters with Special Functionality Some characters have special functionality and need to be treated with extra care. If you experience some unexpected behavior when using format string, check if some of t…

To be sure it's not related to a sandboxing issue, can you try this command via Terminal.app while Mp3tag being closed:

defaults delete app.mp3tag.Mp3tag SecurityScopedBookmarks

After that, load the folder (not the individual files) via ⌘O and see if the issue persists.