[Mediawiki-l] db error in dumpBackup.php on 2nd mediawiki instance

[Corrin Letchworth]

I'm running two instances of mediawiki on the same machine (RHEL3x86).
They're in separate directories in the server, and use different
databases on the local mysql server (4.1.18).  Both instances work
fine.

I'm trying to use the dumpBackup.php script (just calling
dumpBackup.php --full):

On the older instance (which uses the default database info, and which
runs an old mediawiki.1.5.6) the dump works fine.

On the newer instance (which uses mediawiki 1.8.2, and different (from
the install default) wgDBname and wgDBuser) the call to dumpBackup.php
fails with

     DB connection error: Unknown error

Other maintenance scripts (e.g. dumpHTML) work fine too.

Perhaps some piece of info is being assumed to be default in
dumpBackup (rather than being picked up from LocalSettings)?

I'm using php 5.1.2, btw.

Any pointers would be appreciated,
Corrin