While trying to install update 241774 I got “Error 25009: The Forefront Identity Manager Synchronization Service setup wizard cannot configure the specified database. Windows NT user or group ‘mydomain\fimsync-service-account‘ not found. Check the name again.”
When I looked at the logins created on the SQL server I could not see my service account. I tried to add it and got the error “The server principal already exists”.
This post told me what I needed to do. The account did in fact already exist in SQL but under a very old name and the only way to detect it was by the SID. Once I identified the problem login I deleted it and re-created it. The FIM update then proceeded without further error.
One thing that is interesting is that I know this account was renamed a long time ago, at least a year, and I know I’ve installed other updates in that time, but this was the first one that baulked at this problem.
Link to resolve is no longer available, use this instead: https://mssqltrek.com/2013/10/18/the-server-principal-already-exists-msg-15025-level-16-state-2-line-1/
Thanks Keith!