Hi @rikademus welcome to the forum. These types of error messages during plugin scan are usually the result of some kind of OS permissions issue. You could try manually running the plugin scan with Scaler 3 closed to see if it succeeds successfully. It is located in: /Users/[NAME]/Library/Scaler Music/Scaler 3/PluginScanner (double click to run).
If you still receive an error message, dry deleting the scan related files from this same directory: plugins.cache, plugins.custom, plugins.ignore, plugins.log. Then please try running the PluginScannner app manually again. You might also need to make sure you user account has read/write permissions for this Scaler 3 folder.
If you still receive an error message, please try performing a clean install with the latest Scaler 3 installer. Clean install instructions are at the bottom of the Known Issues forum page: List of Known Issues, Descriptions, Solutions, Timing