Here's an update. It's looking like a problem in my 'config' table of my existing site.

I installed a brand-new site from scratch. Made all the appropriate patches, installs, etc. The admin menu works perfectly with the fresh install.

I exported the system core tables from the existing database/site and imported them one at a time into the new database/site until it crashed my new sites' admin menu. When I imported the config table it caused the admin menu to revert to the original admin menu for 2.0.16 before the Altsys.

Any ideas which entries could be causing this behavior?

*ack: my module numbers are different between the installs; fyi*