[Plugin: the-events-calendar] Call to undefined function

Something truly weird is going on with a few of my sites, and after nine hours, I’m out of leads. Hoping someone can point me in the right direction.

I have several sites on WP 3.0.1, using WP-Hive and The-Event-Calendar plugins. Everything is kept up to date. When I added a new site tonight, the TEC plugin stopped functioning on the three sites that it is installed on. No update was run, code was mucked with etc.

All I did to add the new site was to add it under WP-Hive, upload the theme, and do a WP import for the data. I am going from same version to same version. It works on my local, but not on the live. The plugin is installed, functions (in that all of my event data is there, and editable), but doesn’t display. At ALL.

I think I remember an option somewhere a while back that connected the category to the plugin, but I can’t find that now, and I feel like that’s the missing link.

Anyone have any ideas I can try? I’ve uninstalled, reinstalled, wiped the site, reinstalled that, changed the category names, looked through the database for obvious problems, etc…I’m flat-out stuck.

The only clue I get is the following error:
Fatal error: Call to undefined function: the_event_start_date() in .../htdocs/wp-content/themes/Site-Name/index.php on line 22
Which is where I call <?php echo the_event_start_date(); ?> in my index file.

Help.