I have a 3rd party .a library, which is apparently compiled for only armv6 compatibility, where both new Xcodes (3.2.6 and 4), both now require a separate armv7 slice to run
In Project Settings, select "Standard" for the architecture (not "Optimized"). This should allow you to select "armv6" for the Active Architecture. This means it should also work on older devices (barring any other deprecations) once it's on the app store.
Nothing worked for me until I set "Build Active Architecture Only" to No.