[Mediawiki-l] Multiple wikis and resulting database error in Database.php line 1667, on MediaWiki 1.5.0

[Bob Purvy]

after searching diligently through the documentation
for some hint on how to support multiple wikis on the
same site (and finding none), I decided to try just
untarring the distribution into a separate directory
under the Apache home directory.  Sounds safe, right?

i.e. I had been running with everything under
htdocs/wiki, and now I created a htdocs/wiki2 by
untarring, and ran the installation procedure again on
the wiki2, and everything seemed fine, wiki2 was up. 
(I used a separate table prefix for wiki2, so the two
sets of tables are distinct.)

However, now on the original wiki, I get

Fatal error: Call to a member function on a non-object
in
/usr/local/apache2/htdocs/wiki/includes/Database.php
on line 1667

even deleting the wiki2 directory and restarting
Apache doesn't make this go away.

How can I at least get the original wiki back, even if
this strategy for multiple wikis won't work?  Thanks,

Bob