To resolve the issue, reinstall OS X Lion. For instructions, click here.
Aperture 3: iPhoto Browser window may be blank on OS X Lion
When you use Aperture 3 on a computer running OS X Lion, the iPhoto Browser window may be blank. This issue occurs if you install Aperture 2 on the computer running OS X Lion and then upgrade to Aperture 3.
Note: This issue does not occur on computers running Mac OS X v10.6 Snow Leopard with Aperture 2.1.4 which are then upgraded to OS X Lion.