Symptoms

Upgrading from K2 blackpearl 0807 - 690 directly to K2 blackpearl 4.6.6 fails. (Even though the compatibility matrix stated that the upgrade path is valid and supported.)
 

Diagnoses

After some investigations, we found that the "SourceCode.Data.SmartBroker_4_6.upgrade.sql" script broke because it did not find the "AuthenticationPassword" column in the SmartBroker].kServiceInstance] table. This caused the DB upgrade part of the install to fail, while still dropping the assemblies on the machine. This caused the new assemblies to look for entries in the DB that did not exist.
 

Resolution

Recommended approach, is to
- Restore the K2 blackpearl 0807 - 690 DBs.
- Remove the broken 4.6.6 K2Server component
- Get the 0807 - 690 K2Server up and running again with the 0807 690 DBs.
(Basically get yourself back to the state you were before upgrade.)

- After that, perform an upgrade to K2 blackpearl 4.5 with 1420
- Then go to K2 blackpearl 4.6.6.

Additional Information...
I have played around with "fresh" DBs and got the same issue. (Without deploying any K2 processes or any other "modifications") Even with a clean DB, you will still run into the issue. It appears as if it does not have anything to do with the amount of smartbroker services instances, or even a specific type of service instance.

Recommended upgrade path is 0807 - 690 > 4.5 with 1420 > 4.6.6.