I had the same problem today getting the "verification failed" message on 13.2 drivers and then having guiminer and every other miner crash on start up after switching to older drivers.

What I did was uninstall all AMD software/drivers, reboot and install catalyst 13.1 drivers.

Then I followed the steps listed here: http://forums.guru3d.com/showthread.php?t=359883 and now it's working fine.