If you don't have an old enough svnadmin binary, you'll get this error:

$ svnadmin dump .

svnadmin: Berkeley DB error for filesystem 'db' while opening environment:

svnadmin: DB_VERSION_MISMATCH: Database environment version mismatch

svnadmin: bdb: Program version 4.8 doesn't match environment version 4.4

Solution: find a machine (e.g: hardy) with db4.4-util and convert to 4.6. Then find another machine with db4.8-util and convert (ok, maybe I could have converted directly to 4.8, not sure)

Thanks to Uwe Hermann.