This is a solved problem which I hope help others:
After upgrading xcode to 4.5 and devices to ios6, the build on all my working projects (AGK, cordova and Shiva) failed when testing on the device (built and ran fine on simulator 6.0), I had this error:
ld: file is universal (3 slices) but does not contain a(n) armv7s slice: /file/location for architecture armv7s clang: error: linker command failed with exit code 1 (use -v to see invocation)
Upon further investigation I found that the problem is solved by removing the armv7s "Architectures" on Build Settings, as well as in the "Valid Architectures" lines. This is on the project item and on the Target item (these appear on file view, clicking on project root)
Only armv7 should remain until the AppGameKit library has an armv7s slice.(I guess!)
So far all seemed to have returned to normal by changing these settings.
May the 3d force B with U