We followed the instructions for upgrading, but can no longer access the admin control panel. The permissions all seem to be correct and the db.ini file is identical. The backup of the 1.21 install still runs fine in a separate directory. Any ideas on how to troubleshoot this would be appreciated.
This sounds like a mod_rewrite problem.
You may need to add RewriteBase rules to the .htaccess files of your Omeka installation -- perhaps you did this in your old install, and never transferred the changes? There are .htaccess files in both the base directory /, and /admin/.
Turns out I was missing the theme file from the 1.2 site.