This error appears very frequently in the engine.log.
2013-01-22 15:33:10,837 ERROR [org.ovirt.engine.core.engineencryptutils.EncryptionUtils] (MSC service thread 1-5) Failed to decrypt Data must start with zero
2013-01-22 15:33:10,838 ERROR [org.ovirt.engine.core.dal.dbbroker.generic.DBConfigUtils] (MSC service thread 1-5) Failed to decrypt value for property TruststorePass will be used encrypted value
2013-01-22 15:33:10,865 ERROR [org.ovirt.engine.core.engineencryptutils.EncryptionUtils] (MSC service thread 1-5) Failed to decrypt Data must start with zero
2013-01-22 15:33:10,866 ERROR [org.ovirt.engine.core.dal.dbbroker.generic.DBConfigUtils] (MSC service thread 1-5) Failed to decrypt value for property AdminPassword will be used encrypted value
Starting appearing after manual edit to the "AdminPassword" value in the database.
Tried using engine-config -s AdminPassword='somepassword' to change it which always resulted in: cannot set value 'somepassword' to key AdminPassword.