Lookout 6.x uses Citadel 5 database, but Lookout 5.x uses Citadel 4. They are not compatible. Lookout tries to get the database in that folder, but it cannot find Citadel 5 database.
Follow this KB to convert the Citadel 4 to Citadel 5.
You'd better backup the database first.
Or if you don't want the old database any more, you can just configure your process to use the Citadel 5 database in Lookout 6.x folder. Or you can create new database in any folder by MAX, and use it.