Did you install 10.5 client on 10.4 Server?
I've only seen upgradedb error messages on server. Are you trying to upgrade mail databases? (
p. 42)
This is for 10.4 upgrade but unless they changed the location of the Server's core services, it should still be valid.
If it's on normal Mac OS X 10.5 client, which application launches this upgradedb message? Some database is trying to upgrade itself, and it would be good to know what it was.
Open Console (Applications/Utilities) when it starts to give this error again, and then look at Console to see what it says (post the code it will generate then, it will contain what asked for what in your system).