Quoting Mark Lord from the "Merry Christmas" thread in General:

After your v3alpha boots, do a SYNC from emplode to write the databases to disk (on boot, they are not written to disk -- read-only filesystem).

After the sync, v3alpha5 should work just fine.

You mgiht want to keep sync'ing in 3Alpha until it can boot from a power-up without needing to "Rebuild the Database". This will ensure it's properly built.