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.
$ cd /path/to/myrepo/db
$ db4.4_checkpoint -1
$ svnlook youngest ..
$ db4.6_archive -d