How to reset the AU validation.

Digital Performer V5:
Trash the "Audio Unit Info Cache" file and then relaunch Digital Performer:
Macintosh HD / Users / 'Your Account' / Library / Preferences / Digital Performer™ / Audio Unit Info Cache

Digital Performer V6 or higher:
Go to the Digital Performer menu > Preferences:
In the Preferences window, select 'Audio Plug-Ins', find the plug-in in the list and click on the Reexamine button
More Info available at MOTU website : http://www.motu.com/products/software/dp/au-plugin.html

Logic Pro:
Go to the Logic application menu > Preferences > Audio Units Manager.
Find the plugin in the list and click on the "Rescan" button.