wp-admin of secondary blogs runs super slow

I recently upgraded my WP MU site to WP 3.1 Everything seems to be running fine except in the back-end. I have two blogs total and they both respond and work as expected on the front-end. However, when I try to go to the dashboard or any other area in the wp-admin of the secondary site, it takes an abnormal amount of time to load; like, anywhere from 45 seconds to 2 minutes.

I’ve tried disabling all my plugins, removing the new admin bar, etc., but I’m having no luck. I also tried to automatically upgrade my sites by running the Update Network functionality, but I get this error when I try:

Warning! Problem updating ... Your server may not be able to connect to sites running on it. Error message: Could not open handle for fopen() to https://mysite.com/secondaryblog/wp-admin/upgrade.php?step=upgrade_db