Duplicate blogs: one can’t connect to database

It’s me again:

I’m helping a man who had several WP 2.0.2 blog get updated to 2.3.3. Copied one down off his server so I’d have a backup, then put it back up there again with a new name, leaving the old one in situ in the event of a disaster, and sure enough, I’ve got a disaster! (Years of learning have taught me to be prepared!) I ran the updater, or tried to, but I got the dreaded:

We were able to connect to the database server (which means your username and password is okay) but not able to select the example_com_-_wordpress2_v1U2I47o database.

Are you sure it exists?
Does the user example have permission to use the example_com_-_wordpress2_v1U2I47o database?
On some systems the name of your database is prefixed with your username, so it would be like username_wordpress. Could that be the problem?

I’d been tempted to go in to tear down and recreate his database, but now here’s the thing: the old 2.0.2 blog I left in place is using the same database, and has the same info in the config file, so that seems not to be the problem. I even copied the config file over from the 2.0.2 blog just in case I’d made a copy/paste error, but I continue to get the same danged error. This is making no sense to me. Is this ringing any bells with anyone?

Binky