Error establishing database connection

Hello. I’ve seen some other posts with similar titles, but they haven’t resolved my issue. I’ve had a blog running successfully at http://behindthecurtain.us for a few years. Yesterday, I upgraded to 3.0.3. The upgrade appeared to work fine.

I installed a new blog for a friend yesterday. I’ve run multiple blogs with different database prefixes just fine, so know that works. I have a weird feeling it may play into this problem.

So after finishing upgrading everything, I went to behindthecurtain.us just to make sure it still worked. It did. However, right after that, the site failed. I see wp-cron.php executing in the log, then that does it, after that the errors start.
“POST /wp-cron.php?doing_wp_cron HTTP/1.0”

Now I just get an error 500 establishing a database connection. I’ve verified the settings in wp-config.php. I can connect to the database with the mysql client, so I know that works. I made double sure I didn’t alter any of behindthecurtain’s tables when I installed the new blog. I tried a fresh copy of WordPress, both 3.0.3 and 3.0. The error log doesn’t show anything out of the ordinary.

I’d appreciate any help anyone can give. I don’t know if the upgrade caused it, or installing the new site, or perhaps some combination.