[Vilemare]

Got that one once. AI is using the custom shipset you added, and missing the 5 AI-files which descibe the race: DesingCreation, Fleets, General, Research and Settings. Copy those 5 txt files from some existing race, rename them according the custom set name and do some creative editing in the AI_General file (or do them all if you want to). I don't think you can restore the empire in your current saved game, but on the next campaing the AI is able the use the custom shipset and race correctly.