Critical Bug Fixed: "'mt_pluginmanager' doesn't exist"
It took me far too long to track down a simple error a number of people were reporting with Plugin Manager, but I did track it down, and did finally manage to fix it. Long story short, the deployment mechanism I wrote to distribute new versions of the software out to the servers was faulty and was failing to update a single, but critical file. As a result users continued to download an arcane version of PluginManager.pl as opposed to the latest and greatest. Without the newer version, Plugin Manager was never able to initialize itself properly and thus failed to load.
But again, that issue has been resolved. Plugin Manager's install script should work just fine again. My apologies for the inconvenience this may have caused many of you.