Logic Pro/Express 9: 32-bit Audio Unit plug-ins may not be available in 64-bit mode after updating to OS X Lion
After updating to OS X Lion, some of your 32-bit Audio Unit plug-ins may not be available if you are using Logic in 64-bit mode.
Open Logic Pro or Express in 32-bit mode to scan the 32-bit Audio Unit plug-ins. After they have been scanned in 32-bit mode, they will be available in either 32-bit or 64-bit mode.
See the Logic Pro and MainStage 64-bit FAQ for instructions on how to switch between 32-bit and 64-bit mode.