I successfully flashed boot.img from latest nighly (thnks btw).
I flashed cm9.zip, fatory-reset, gapps, fatory-reset, reboot...
Had this too, a while ago, the only thing helped is:
- Flash stock
- Flash CM7 (latest)
- Flash CM9 (+ GApps, kernel etc), wipe cache and fix permissions
= WIN
But this was due the fact I did a stupid thing, guess it's not the
same as for you, very weird it did not do the trick by restoring
the Nandroid and/or flash CM9 again. It is also possible to format
/BOOT and /SYSTEM through the CWM (but don't reboot after
that and do immediately a new CM9 or CM7 flash).