Audio Unit errors display error mesages when trying to load the instrument with the standalone application, or in a DAW. Here are a few examples:
If you are receiving any errors referring to Audio Units, first make sure that the .component file for your instrument is showing up in this location:
Macintosh HD/ Library/ Audio/ Plug-Ins/ Components/
If it is present, restart your computer and this should resolve this issue.
If you do not see it, download and install the latest software update for your instrument from your user account, confirm that it was installed to the above location, and then restart your computer.